563 lines
18 KiB
Python
563 lines
18 KiB
Python
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"""Pygame Drawing algorithms written in Python. (Work in Progress)
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Implement Pygame's Drawing Algorithms in a Python version for testing
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and debugging.
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"""
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from collections import namedtuple
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from math import floor, ceil
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# H E L P E R F U N C T I O N S #
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# fractional part of x
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def frac(value):
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"""return fractional part of x"""
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return value - floor(value)
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def inv_frac(value):
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"""return inverse fractional part of x"""
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return 1 - (value - floor(value)) # eg, 1 - frac(x)
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BoundingBox = namedtuple("BoundingBox", ["left", "top", "right", "bottom"])
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Point = namedtuple("Point", ["x", "y"])
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# L O W L E V E L D R A W F U N C T I O N S #
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# (They are too low-level to be translated into python, right?)
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def set_at(surf, in_x, in_y, color):
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"""Set the color of a pixel in a surface"""
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surf.set_at((in_x, in_y), color)
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def draw_pixel(surf, pos, color, bright, blend=True):
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"""draw one blended pixel with given brightness."""
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try:
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other_col = surf.get_at(pos) if blend else (0, 0, 0, 0)
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except IndexError: # pixel outside the surface
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return
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new_color = tuple(
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(bright * col + (1 - bright) * pix) for col, pix in zip(color, other_col)
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)
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# FIXME what should happen if only one, color or surf_col, has alpha?
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surf.set_at(pos, new_color)
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def _drawhorzline(surf, color, x_from, in_y, x_to):
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if x_from == x_to:
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surf.set_at((x_from, in_y), color)
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return
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start, end = (x_from, x_to) if x_from <= x_to else (x_to, x_from)
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for line_x in range(start, end + 1):
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surf.set_at((line_x, in_y), color)
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def _drawvertline(surf, color, in_x, y_from, y_to):
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if y_from == y_to:
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surf.set_at((in_x, y_from), color)
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return
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start, end = (y_from, y_to) if y_from <= y_to else (y_to, y_from)
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for line_y in range(start, end + 1):
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surf.set_at((in_x, line_y), color)
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# I N T E R N A L D R A W L I N E F U N C T I O N S #
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def _clip_and_draw_horizline(surf, color, x_from, in_y, x_to):
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"""draw clipped horizontal line."""
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# check Y inside surf
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clip = surf.get_clip()
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if in_y < clip.y or in_y >= clip.y + clip.h:
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return
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x_from = max(x_from, clip.x)
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x_to = min(x_to, clip.x + clip.w - 1)
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# check any x inside surf
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if x_to < clip.x or x_from >= clip.x + clip.w:
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return
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_drawhorzline(surf, color, x_from, in_y, x_to)
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def _clip_and_draw_vertline(surf, color, in_x, y_from, y_to):
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"""draw clipped vertical line."""
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# check X inside surf
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clip = surf.get_clip()
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if in_x < clip.x or in_x >= clip.x + clip.w:
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return
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y_from = max(y_from, clip.y)
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y_to = min(y_to, clip.y + clip.h - 1)
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# check any y inside surf
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if y_to < clip.y or y_from >= clip.y + clip.h:
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return
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_drawvertline(surf, color, in_x, y_from, y_to)
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# These constants xxx_EDGE are "outside-the-bounding-box"-flags
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LEFT_EDGE = 0x1
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RIGHT_EDGE = 0x2
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BOTTOM_EDGE = 0x4
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TOP_EDGE = 0x8
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def encode(pos, b_box):
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"""returns a code that defines position with respect to a bounding box"""
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# we use the fact that python interprets booleans (the inequalities)
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# as 0/1, and then multiply them with the xxx_EDGE flags
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return (
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(pos[0] < b_box.left) * LEFT_EDGE
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+ (pos[0] > b_box.right) * RIGHT_EDGE
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+ (pos[1] < b_box.top) * TOP_EDGE
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+ (pos[1] > b_box.bottom) * BOTTOM_EDGE
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)
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def clip_line(line, b_box, use_float=False):
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"""Algorithm to calculate the clipped line.
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We calculate the coordinates of the part of the line segment within the
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bounding box (defined by left, top, right, bottom). The we write
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the coordinates of the line segment into "line", much like the C-algorithm.
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With `use_float` True, clip_line is usable for float-clipping.
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Returns: true if the line segment cuts the bounding box (false otherwise)
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"""
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def inside(code):
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return not code
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def accept(code_a, code_b):
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return not (code_a or code_b)
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def reject(code_a, code_b):
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return code_a and code_b
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assert isinstance(line, list)
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x_1, y_1, x_2, y_2 = line
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dtype = float if use_float else int
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while True:
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# the coordinates are progressively modified with the codes,
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# until they are either rejected or correspond to the final result.
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code1 = encode((x_1, y_1), b_box)
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code2 = encode((x_2, y_2), b_box)
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if accept(code1, code2):
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# write coordinates into "line" !
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line[:] = x_1, y_1, x_2, y_2
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return True
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if reject(code1, code2):
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return False
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# We operate on the (x_1, y_1) point,
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# and swap if it is inside the bbox:
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if inside(code1):
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x_1, x_2 = x_2, x_1
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y_1, y_2 = y_2, y_1
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code1, code2 = code2, code1
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slope = (y_2 - y_1) / float(x_2 - x_1) if (x_2 != x_1) else 1.0
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# Each case, if true, means that we are outside the border:
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# calculate x_1 and y_1 to be the "first point" inside the bbox...
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if code1 & LEFT_EDGE:
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y_1 += dtype((b_box.left - x_1) * slope)
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x_1 = b_box.left
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elif code1 & RIGHT_EDGE:
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y_1 += dtype((b_box.right - x_1) * slope)
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x_1 = b_box.right
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elif code1 & BOTTOM_EDGE:
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if x_2 != x_1:
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x_1 += dtype((b_box.bottom - y_1) / slope)
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y_1 = b_box.bottom
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elif code1 & TOP_EDGE:
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if x_2 != x_1:
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x_1 += dtype((b_box.top - y_1) / slope)
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y_1 = b_box.top
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def _draw_line(surf, color, start, end):
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"""draw a non-horizontal line (without anti-aliasing)."""
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# Variant of https://en.wikipedia.org/wiki/Bresenham's_line_algorithm
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#
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# This strongly differs from craw.c implementation, because we use a
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# "slope" variable (instead of delta_x and delta_y) and a "error" variable.
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# And we can not do pointer-arithmetic with "BytesPerPixel", like in
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# the C-algorithm.
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if start.x == end.x:
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# This case should not happen...
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raise ValueError
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slope = abs((end.y - start.y) / (end.x - start.x))
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error = 0.0
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if slope < 1:
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# Here, it's a rather horizontal line
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# 1. check in which octants we are & set init values
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if end.x < start.x:
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start.x, end.x = end.x, start.x
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start.y, end.y = end.y, start.y
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line_y = start.y
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dy_sign = 1 if (start.y < end.y) else -1
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# 2. step along x coordinate
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for line_x in range(start.x, end.x + 1):
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set_at(surf, line_x, line_y, color)
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error += slope
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if error >= 0.5:
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line_y += dy_sign
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error -= 1
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else:
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# Case of a rather vertical line
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# 1. check in which octants we are & set init values
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if start.y > end.y:
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start.x, end.x = end.x, start.x
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start.y, end.y = end.y, start.y
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line_x = start.x
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slope = 1 / slope
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dx_sign = 1 if (start.x < end.x) else -1
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# 2. step along y coordinate
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for line_y in range(start.y, end.y + 1):
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set_at(surf, line_x, line_y, color)
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error += slope
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if error >= 0.5:
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line_x += dx_sign
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error -= 1
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def _draw_aaline(surf, color, start, end, blend):
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"""draw an anti-aliased line.
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The algorithm yields identical results with _draw_line for horizontal,
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vertical or diagonal lines, and results changes smoothly when changing
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any of the endpoint coordinates.
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Note that this yields strange results for very short lines, eg
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a line from (0, 0) to (0, 1) will draw 2 pixels, and a line from
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(0, 0) to (0, 1.1) will blend 10 % on the pixel (0, 2).
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"""
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# The different requirements that we have on an antialiasing algorithm
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# implies to make some compromises:
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# 1. We want smooth evolution wrt to the 4 endpoint coordinates
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# (this means also that we want a smooth evolution when the angle
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# passes +/- 45°
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# 2. We want the same behavior when swapping the endpoints
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# 3. We want understandable results for the endpoint values
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# (eg we want to avoid half-integer values to draw a simple plain
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# horizontal or vertical line between two integer l endpoints)
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#
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# This implies to somehow make the line artificially 1 pixel longer
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# and to draw a full pixel when we have the endpoints are identical.
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d_x = end.x - start.x
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d_y = end.y - start.y
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if d_x == 0 and d_y == 0:
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# For smoothness reasons, we could also do some blending here,
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# but it seems overshoot...
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set_at(surf, int(start.x), int(start.y), color)
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return
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if start.x > end.x or start.y > end.y:
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start.x, end.x = end.x, start.x
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start.y, end.y = end.y, start.y
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d_x = -d_x
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d_y = -d_y
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if abs(d_x) >= abs(d_y):
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slope = d_y / d_x
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def draw_two_pixel(in_x, float_y, factor):
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flr_y = floor(float_y)
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draw_pixel(surf, (in_x, flr_y), color, factor * inv_frac(float_y), blend)
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draw_pixel(surf, (in_x, flr_y + 1), color, factor * frac(float_y), blend)
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_draw_aaline_dx(d_x, slope, end, start, draw_two_pixel)
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else:
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slope = d_x / d_y
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def draw_two_pixel(float_x, in_y, factor):
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fl_x = floor(float_x)
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draw_pixel(surf, (fl_x, in_y), color, factor * inv_frac(float_x), blend)
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draw_pixel(surf, (fl_x + 1, in_y), color, factor * frac(float_x), blend)
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_draw_aaline_dy(d_y, slope, end, start, draw_two_pixel)
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def _draw_aaline_dy(d_y, slope, end, start, draw_two_pixel):
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g_y = ceil(start.y)
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g_x = start.x + (g_y - start.y) * slope
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# 1. Draw start of the segment
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if start.y < g_y:
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draw_two_pixel(g_x - slope, floor(start.y), inv_frac(start.y))
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# 2. Draw end of the segment
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rest = frac(end.y)
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s_y = ceil(end.y)
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if rest > 0:
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s_x = start.x + slope * (d_y + 1 - rest)
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draw_two_pixel(s_x, s_y, rest)
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else:
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s_y += 1
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# 3. loop for other points
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for line_y in range(g_y, s_y):
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line_x = g_x + slope * (line_y - g_y)
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draw_two_pixel(line_x, line_y, 1)
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def _draw_aaline_dx(d_x, slope, end, start, draw_two_pixel):
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# A and G are respectively left and right to the "from" point, but
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# with integer-x-coordinate, (and only if from_x is not integer).
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# Hence they appear in following order on the line in general case:
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# A from-pt G . . . to-pt S
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# |------*-------|--- . . . ---|-----*------|-
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g_x = ceil(start.x)
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g_y = start.y + (g_x - start.x) * slope
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# 1. Draw start of the segment if we have a non-integer-part
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if start.x < g_x:
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# this corresponds to the point "A"
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draw_two_pixel(floor(start.x), g_y - slope, inv_frac(start.x))
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# 2. Draw end of the segment: we add one pixel for homogeneity reasons
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rest = frac(end.x)
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s_x = ceil(end.x)
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if rest > 0:
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# Again we draw only if we have a non-integer-part
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s_y = start.y + slope * (d_x + 1 - rest)
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draw_two_pixel(s_x, s_y, rest)
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else:
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s_x += 1
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# 3. loop for other points
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for line_x in range(g_x, s_x):
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line_y = g_y + slope * (line_x - g_x)
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draw_two_pixel(line_x, line_y, 1)
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# C L I P A N D D R A W L I N E F U N C T I O N S #
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def _clip_and_draw_line(surf, rect, color, pts):
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"""clip the line into the rectangle and draw if needed.
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Returns true if anything has been drawn, else false."""
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# "pts" is a list with the four coordinates of the two endpoints
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# of the line to be drawn : pts = x1, y1, x2, y2.
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# The data format is like that to stay closer to the C-algorithm.
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if not clip_line(
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pts, BoundingBox(rect.x, rect.y, rect.x + rect.w - 1, rect.y + rect.h - 1)
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):
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# The line segment defined by "pts" is not crossing the rectangle
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return 0
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if pts[1] == pts[3]: # eg y1 == y2
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_drawhorzline(surf, color, pts[0], pts[1], pts[2])
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elif pts[0] == pts[2]: # eg x1 == x2
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_drawvertline(surf, color, pts[0], pts[1], pts[3])
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else:
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_draw_line(surf, color, Point(pts[0], pts[1]), Point(pts[2], pts[3]))
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return 1
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def _clip_and_draw_line_width(surf, rect, color, line, width):
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yinc = xinc = 0
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if abs(line[0] - line[2]) > abs(line[1] - line[3]):
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yinc = 1
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else:
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xinc = 1
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newpts = line[:]
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if _clip_and_draw_line(surf, rect, color, newpts):
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anydrawn = 1
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frame = newpts[:]
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else:
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anydrawn = 0
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frame = [10000, 10000, -10000, -10000]
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for loop in range(1, width // 2 + 1):
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newpts[0] = line[0] + xinc * loop
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newpts[1] = line[1] + yinc * loop
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newpts[2] = line[2] + xinc * loop
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newpts[3] = line[3] + yinc * loop
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if _clip_and_draw_line(surf, rect, color, newpts):
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anydrawn = 1
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frame[0] = min(newpts[0], frame[0])
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frame[1] = min(newpts[1], frame[1])
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frame[2] = max(newpts[2], frame[2])
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frame[3] = max(newpts[3], frame[3])
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if loop * 2 < width:
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newpts[0] = line[0] - xinc * loop
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newpts[1] = line[1] - yinc * loop
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newpts[2] = line[2] - xinc * loop
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newpts[3] = line[3] - yinc * loop
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if _clip_and_draw_line(surf, rect, color, newpts):
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anydrawn = 1
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frame[0] = min(newpts[0], frame[0])
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frame[1] = min(newpts[1], frame[1])
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frame[2] = max(newpts[2], frame[2])
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frame[3] = max(newpts[3], frame[3])
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return anydrawn
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def _clip_and_draw_aaline(surf, rect, color, line, blend):
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"""draw anti-aliased line between two endpoints."""
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if not clip_line(
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line,
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BoundingBox(rect.x - 1, rect.y - 1, rect.x + rect.w, rect.y + rect.h),
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use_float=True,
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):
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return # TODO Rect(rect.x, rect.y, 0, 0)
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_draw_aaline(surf, color, Point(line[0], line[1]), Point(line[2], line[3]), blend)
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return # TODO Rect(-- affected area --)
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# D R A W L I N E F U N C T I O N S #
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def draw_aaline(surf, color, from_point, to_point, blend=True):
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"""draw anti-aliased line between two endpoints."""
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line = [from_point[0], from_point[1], to_point[0], to_point[1]]
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return _clip_and_draw_aaline(surf, surf.get_clip(), color, line, blend)
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def draw_line(surf, color, from_point, to_point, width=1):
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"""draw anti-aliased line between two endpoints."""
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line = [from_point[0], from_point[1], to_point[0], to_point[1]]
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return _clip_and_draw_line_width(surf, surf.get_clip(), color, line, width)
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# M U L T I L I N E F U N C T I O N S #
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def _multi_lines(
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surf,
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color,
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closed, # pylint: disable=too-many-arguments
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points,
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width=1,
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blend=False,
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aaline=False,
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):
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"""draw several lines, either anti-aliased or not."""
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# The code for anti-aliased or not is almost identical, so it's factorized
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if len(points) <= 2:
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raise TypeError
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line = [0] * 4 # store x1, y1 & x2, y2 of the lines to be drawn
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xlist = [pt[0] for pt in points]
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ylist = [pt[1] for pt in points]
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line[0] = xlist[0]
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line[1] = ylist[0]
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b_box = BoundingBox(left=xlist[0], right=xlist[0], top=ylist[0], bottom=ylist[0])
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for line_x, line_y in points[1:]:
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b_box.left = min(b_box.left, line_x)
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b_box.right = max(b_box.right, line_x)
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b_box.top = min(b_box.top, line_y)
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b_box.bottom = max(b_box.bottom, line_y)
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rect = surf.get_clip()
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for loop in range(1, len(points)):
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line[0] = xlist[loop - 1]
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line[1] = ylist[loop - 1]
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line[2] = xlist[loop]
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line[3] = ylist[loop]
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if aaline:
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_clip_and_draw_aaline(surf, rect, color, line, blend)
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else:
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_clip_and_draw_line_width(surf, rect, color, line, width)
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if closed:
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line[0] = xlist[len(points) - 1]
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line[1] = ylist[len(points) - 1]
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line[2] = xlist[0]
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line[3] = ylist[0]
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if aaline:
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_clip_and_draw_aaline(surf, rect, color, line, blend)
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else:
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_clip_and_draw_line_width(surf, rect, color, line, width)
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# TODO Rect(...)
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def draw_lines(surf, color, closed, points, width=1):
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"""draw several lines connected through the points."""
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return _multi_lines(surf, color, closed, points, width, aaline=False)
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def draw_aalines(surf, color, closed, points, blend=True):
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"""draw several anti-aliased lines connected through the points."""
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return _multi_lines(surf, color, closed, points, blend=blend, aaline=True)
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def draw_polygon(surface, color, points, width):
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"""Draw a polygon"""
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if width:
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draw_lines(surface, color, 1, points, width)
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return # TODO Rect(...)
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num_points = len(points)
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point_x = [x for x, y in points]
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point_y = [y for x, y in points]
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miny = min(point_y)
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maxy = max(point_y)
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if miny == maxy:
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minx = min(point_x)
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maxx = max(point_x)
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_clip_and_draw_horizline(surface, color, minx, miny, maxx)
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return # TODO Rect(...)
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for y_coord in range(miny, maxy + 1):
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x_intersect = []
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for i in range(num_points):
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_draw_polygon_inner_loop(i, point_x, point_y, y_coord, x_intersect)
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x_intersect.sort()
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for i in range(0, len(x_intersect), 2):
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_clip_and_draw_horizline(
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surface, color, x_intersect[i], y_coord, x_intersect[i + 1]
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)
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# special case : horizontal border lines
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for i in range(num_points):
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i_prev = i - 1 if i else num_points - 1
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if miny < point_y[i] == point_y[i_prev] < maxy:
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_clip_and_draw_horizline(
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surface, color, point_x[i], point_y[i], point_x[i_prev]
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)
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return # TODO Rect(...)
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def _draw_polygon_inner_loop(index, point_x, point_y, y_coord, x_intersect):
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i_prev = index - 1 if index else len(point_x) - 1
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y_1 = point_y[i_prev]
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y_2 = point_y[index]
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if y_1 < y_2:
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x_1 = point_x[i_prev]
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x_2 = point_x[index]
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elif y_1 > y_2:
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y_2 = point_y[i_prev]
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y_1 = point_y[index]
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x_2 = point_x[i_prev]
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x_1 = point_x[index]
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else: # special case handled below
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return
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if (y_2 > y_coord >= y_1) or ((y_coord == max(point_y)) and (y_coord <= y_2)):
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x_intersect.append((y_coord - y_1) * (x_2 - x_1) // (y_2 - y_1) + x_1)
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