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Only prevent repeated polygon pixels when drawing with transparency #5835

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merged 2 commits into from Nov 16, 2021
Merged

Only prevent repeated polygon pixels when drawing with transparency #5835

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ca15c68
Only prevent repeated polygon pixels when drawing with transparency
radarhere Nov 15, 2021
d7873e0
Added test that translucent polygon pixels do not combine
radarhere Nov 16, 2021
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Binary file added Tests/images/imagedraw_polygon_translucent.png
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13 changes: 13 additions & 0 deletions Tests/test_imagedraw.py
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Expand Up @@ -638,6 +638,19 @@ def test_polygon_1px_high():
assert_image_equal_tofile(im, expected)


def test_polygon_translucent():
# Arrange
im = Image.new("RGB", (W, H))
draw = ImageDraw.Draw(im, "RGBA")

# Act
draw.polygon([(20, 80), (80, 80), (80, 20)], fill=(0, 255, 0, 127))

# Assert
expected = "Tests/images/imagedraw_polygon_translucent.png"
assert_image_equal_tofile(im, expected)


def helper_rectangle(bbox):
# Arrange
im = Image.new("RGB", (W, H))
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61 changes: 35 additions & 26 deletions src/libImaging/Draw.c
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Expand Up @@ -444,7 +444,7 @@ draw_horizontal_lines(
* Filled polygon draw function using scan line algorithm.
*/
static inline int
polygon_generic(Imaging im, int n, Edge *e, int ink, int eofill, hline_handler hline) {
polygon_generic(Imaging im, int n, Edge *e, int ink, int eofill, hline_handler hline, int hasAlpha) {
Edge **edge_table;
float *xx;
int edge_count = 0;
Expand All @@ -471,6 +471,9 @@ polygon_generic(Imaging im, int n, Edge *e, int ink, int eofill, hline_handler h
ymax = e[i].ymax;
}
if (e[i].ymin == e[i].ymax) {
if (hasAlpha != 1) {
(*hline)(im, e[i].xmin, e[i].ymin, e[i].xmax, ink);
}
continue;
}
edge_table[edge_count++] = (e + i);
Expand All @@ -491,7 +494,6 @@ polygon_generic(Imaging im, int n, Edge *e, int ink, int eofill, hline_handler h
}
for (; ymin <= ymax; ymin++) {
int j = 0;
int x_pos = 0;
for (i = 0; i < edge_count; i++) {
Edge *current = edge_table[i];
if (ymin >= current->ymin && ymin <= current->ymax) {
Expand All @@ -504,31 +506,38 @@ polygon_generic(Imaging im, int n, Edge *e, int ink, int eofill, hline_handler h
}
}
qsort(xx, j, sizeof(float), x_cmp);
for (i = 1; i < j; i += 2) {
int x_end = ROUND_DOWN(xx[i]);
if (x_end < x_pos) {
// Line would be before the current position
continue;
}
draw_horizontal_lines(im, n, e, ink, &x_pos, ymin, hline);
if (x_end < x_pos) {
// Line would be before the current position
continue;
}

int x_start = ROUND_UP(xx[i - 1]);
if (x_pos > x_start) {
// Line would be partway through x_pos, so increase the starting point
x_start = x_pos;
if (x_end < x_start) {
// Line would now end before it started
if (hasAlpha == 1) {
int x_pos = 0;
for (i = 1; i < j; i += 2) {
int x_end = ROUND_DOWN(xx[i]);
if (x_end < x_pos) {
// Line would be before the current position
continue;
}
draw_horizontal_lines(im, n, e, ink, &x_pos, ymin, hline);
if (x_end < x_pos) {
// Line would be before the current position
continue;
}

int x_start = ROUND_UP(xx[i - 1]);
if (x_pos > x_start) {
// Line would be partway through x_pos, so increase the starting point
x_start = x_pos;
if (x_end < x_start) {
// Line would now end before it started
continue;
}
}
(*hline)(im, x_start, ymin, x_end, ink);
x_pos = x_end + 1;
}
draw_horizontal_lines(im, n, e, ink, &x_pos, ymin, hline);
} else {
for (i = 1; i < j; i += 2) {
(*hline)(im, ROUND_UP(xx[i - 1]), ymin, ROUND_DOWN(xx[i]), ink);
}
(*hline)(im, x_start, ymin, x_end, ink);
x_pos = x_end + 1;
}
draw_horizontal_lines(im, n, e, ink, &x_pos, ymin, hline);
}

free(xx);
Expand All @@ -538,17 +547,17 @@ polygon_generic(Imaging im, int n, Edge *e, int ink, int eofill, hline_handler h

static inline int
polygon8(Imaging im, int n, Edge *e, int ink, int eofill) {
return polygon_generic(im, n, e, ink, eofill, hline8);
return polygon_generic(im, n, e, ink, eofill, hline8, 0);
}

static inline int
polygon32(Imaging im, int n, Edge *e, int ink, int eofill) {
return polygon_generic(im, n, e, ink, eofill, hline32);
return polygon_generic(im, n, e, ink, eofill, hline32, 0);
}

static inline int
polygon32rgba(Imaging im, int n, Edge *e, int ink, int eofill) {
return polygon_generic(im, n, e, ink, eofill, hline32rgba);
return polygon_generic(im, n, e, ink, eofill, hline32rgba, 1);
}

static inline void
Expand Down