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LibGfx: Prevent out of bounds access when scaling small Bitmaps

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Since the color interpolation requires two pixels in the horizontal and
vertical direction to work, 1 pixel wide or high bitmaps would cause a
crash when scaling. Fix this by clamping the index into the valid range.

Fixes #16047.
This commit is contained in:
Darius Arnold 2022-11-16 11:38:51 +01:00 • committed by Andreas Kling
parent 71d5dc510e
commit 884d8b14ac
3 changed files with 226 additions and 49 deletions
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146
Userland/Libraries/LibGfx/Bitmap.cpp
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@ -384,66 +384,114 @@ ErrorOr<NonnullRefPtr<Gfx::Bitmap>> Bitmap::scaled(float sx, float sy) const
auto new_width = new_bitmap->physical_width();
auto new_height = new_bitmap->physical_height();
// The interpolation goes out of bounds on the bottom- and right-most edges.
// We handle those in two specialized loops not only to make them faster, but
// also to avoid four branch checks for every pixel.
if (old_width == 1 && old_height == 1) {
new_bitmap->fill(get_pixel(0, 0));
return new_bitmap;
}
for (int y = 0; y < new_height - 1; y++) {
if (old_width > 1 && old_height > 1) {
// The interpolation goes out of bounds on the bottom- and right-most edges.
// We handle those in two specialized loops not only to make them faster, but
// also to avoid four branch checks for every pixel.
for (int y = 0; y < new_height - 1; y++) {
for (int x = 0; x < new_width - 1; x++) {
auto p = static_cast<float>(x) * static_cast<float>(old_width - 1) / static_cast<float>(new_width - 1);
auto q = static_cast<float>(y) * static_cast<float>(old_height - 1) / static_cast<float>(new_height - 1);
int i = floorf(p);
int j = floorf(q);
float u = p - static_cast<float>(i);
float v = q - static_cast<float>(j);
auto a = get_pixel(i, j);
auto b = get_pixel(i + 1, j);
auto c = get_pixel(i, j + 1);
auto d = get_pixel(i + 1, j + 1);
auto e = a.mixed_with(b, u);
auto f = c.mixed_with(d, u);
auto color = e.mixed_with(f, v);
new_bitmap->set_pixel(x, y, color);
}
}
// Bottom strip (excluding last pixel)
auto old_bottom_y = old_height - 1;
auto new_bottom_y = new_height - 1;
for (int x = 0; x < new_width - 1; x++) {
auto p = static_cast<float>(x) * static_cast<float>(old_width - 1) / static_cast<float>(new_width - 1);
auto q = static_cast<float>(y) * static_cast<float>(old_height - 1) / static_cast<float>(new_height - 1);
int i = floorf(p);
int j = floorf(q);
float u = p - static_cast<float>(i);
auto a = get_pixel(i, old_bottom_y);
auto b = get_pixel(i + 1, old_bottom_y);
auto color = a.mixed_with(b, u);
new_bitmap->set_pixel(x, new_bottom_y, color);
}
// Right strip (excluding last pixel)
auto old_right_x = old_width - 1;
auto new_right_x = new_width - 1;
for (int y = 0; y < new_height - 1; y++) {
auto q = static_cast<float>(y) * static_cast<float>(old_height - 1) / static_cast<float>(new_height - 1);
int j = floorf(q);
float v = q - static_cast<float>(j);
auto a = get_pixel(i, j);
auto b = get_pixel(i + 1, j);
auto c = get_pixel(i, j + 1);
auto d = get_pixel(i + 1, j + 1);
auto c = get_pixel(old_right_x, j);
auto d = get_pixel(old_right_x, j + 1);
auto e = a.mixed_with(b, u);
auto f = c.mixed_with(d, u);
auto color = e.mixed_with(f, v);
new_bitmap->set_pixel(x, y, color);
auto color = c.mixed_with(d, v);
new_bitmap->set_pixel(new_right_x, y, color);
}
// Bottom-right pixel
new_bitmap->set_pixel(new_width - 1, new_height - 1, get_pixel(physical_width() - 1, physical_height() - 1));
return new_bitmap;
} else if (old_height == 1) {
// Copy horizontal strip multiple times (excluding last pixel to out of bounds).
auto old_bottom_y = old_height - 1;
for (int x = 0; x < new_width - 1; x++) {
auto p = static_cast<float>(x) * static_cast<float>(old_width - 1) / static_cast<float>(new_width - 1);
int i = floorf(p);
float u = p - static_cast<float>(i);
auto a = get_pixel(i, old_bottom_y);
auto b = get_pixel(i + 1, old_bottom_y);
auto color = a.mixed_with(b, u);
for (int new_bottom_y = 0; new_bottom_y < new_height; new_bottom_y++) {
// Interpolate color only once and then copy into all columns.
new_bitmap->set_pixel(x, new_bottom_y, color);
}
}
for (int new_bottom_y = 0; new_bottom_y < new_height; new_bottom_y++) {
// Copy last pixel of horizontal strip
new_bitmap->set_pixel(new_width - 1, new_bottom_y, get_pixel(physical_width() - 1, old_bottom_y));
}
return new_bitmap;
} else if (old_width == 1) {
// Copy vertical strip multiple times (excluding last pixel to avoid out of bounds).
auto old_right_x = old_width - 1;
for (int y = 0; y < new_height - 1; y++) {
auto q = static_cast<float>(y) * static_cast<float>(old_height - 1) / static_cast<float>(new_height - 1);
int j = floorf(q);
float v = q - static_cast<float>(j);
auto c = get_pixel(old_right_x, j);
auto d = get_pixel(old_right_x, j + 1);
auto color = c.mixed_with(d, v);
for (int new_right_x = 0; new_right_x < new_width; new_right_x++) {
// Interpolate color only once and copy into all rows.
new_bitmap->set_pixel(new_right_x, y, color);
}
}
for (int new_right_x = 0; new_right_x < new_width; new_right_x++) {
// Copy last pixel of vertical strip
new_bitmap->set_pixel(new_right_x, new_height - 1, get_pixel(old_right_x, physical_height() - 1));
}
}
// Bottom strip (excluding last pixel)
auto old_bottom_y = old_height - 1;
auto new_bottom_y = new_height - 1;
for (int x = 0; x < new_width - 1; x++) {
auto p = static_cast<float>(x) * static_cast<float>(old_width - 1) / static_cast<float>(new_width - 1);
int i = floorf(p);
float u = p - static_cast<float>(i);
auto a = get_pixel(i, old_bottom_y);
auto b = get_pixel(i + 1, old_bottom_y);
auto color = a.mixed_with(b, u);
new_bitmap->set_pixel(x, new_bottom_y, color);
}
// Right strip (excluding last pixel)
auto old_right_x = old_width - 1;
auto new_right_x = new_width - 1;
for (int y = 0; y < new_height - 1; y++) {
auto q = static_cast<float>(y) * static_cast<float>(old_height - 1) / static_cast<float>(new_height - 1);
int j = floorf(q);
float v = q - static_cast<float>(j);
auto c = get_pixel(old_right_x, j);
auto d = get_pixel(old_right_x, j + 1);
auto color = c.mixed_with(d, v);
new_bitmap->set_pixel(new_right_x, y, color);
}
// Bottom-right pixel
new_bitmap->set_pixel(new_width - 1, new_height - 1, get_pixel(physical_width() - 1, physical_height() - 1));
return new_bitmap;
}