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LibSoftGPU: Apply regular cartesian coordinate system

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Currently, LibSoftGPU is still OpenGL-minded in that it uses a
coordinate system with the origin of `(0, 0)` at the lower-left of
textures, buffers and window coordinates. Because we are blitting to a
`Gfx::Bitmap` that has the origin at the top-left, we need to flip the
Y-coordinates somewhere in the rasterization logic.

We used to do this during conversion of NDC-coordinates to window
coordinates. This resulted in some incorrect behavior when
rasterization did not pass through the vertex transformation logic,
e.g. when calling `glDrawPixels`.

This changes the coordinate system to OpenGL's throughout, only to blit
the final color buffer upside down to the target bitmap. This fixes
drawing to the depth buffer directly resulting in upside down images.
This commit is contained in:
Jelle Raaijmakers 2022-01-31 17:45:14 +01:00 • committed by Linus Groh
parent 3832656464
commit 8c9fa50c61
3 changed files with 21 additions and 31 deletions
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6
Userland/Libraries/LibSoftGPU/Buffer/Typed2DBuffer.h
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@ -47,11 +47,13 @@ public:
}
}
void blit_to_bitmap(Gfx::Bitmap& bitmap, Gfx::IntRect const& target) const requires IsSame<T, u32>
void blit_flipped_to_bitmap(Gfx::Bitmap& bitmap, Gfx::IntRect const& target) const requires IsSame<T, u32>
{
VERIFY(bitmap.format() == Gfx::BitmapFormat::BGRA8888 || bitmap.format() == Gfx::BitmapFormat::BGRx8888);
int source_y = 0;
for (int y = target.top(); y <= target.bottom(); ++y) {
// NOTE: we are flipping the Y-coordinate here, which is OpenGL-specific: (0, 0) is considered the lower-left corner of the window
for (int y = target.bottom(); y >= target.top(); --y) {
auto const* buffer_scanline = scanline(source_y++);
auto* bitmap_scanline = bitmap.scanline(y);