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[Impeller] disable overdraw prevention for source draws. (flutter/engine#56403)

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Overdraw prevention prevents overlapping triangles in the stroke tessellator from being visible with partially opaque draws. For fully opaque draws (or usage of src blend mode) I do not believe this will be an issue - so we can disable this to speed things up a tiny bit.

This code runs after we covert opaque draws to src blend mode, so checking for src blend mode should be sufficient.
This commit is contained in:
Jonah Williams 2024-11-07 08:59:21 -08:00 committed by GitHub
parent a6917332f8
commit 7f0892aaeb
1 changed files with 6 additions and 3 deletions
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9
engine/src/flutter/impeller/entity/contents/color_source_contents.h
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@ -232,8 +232,10 @@ class ColorSourceContents : public Contents {
// If overdraw prevention is enabled (like when drawing stroke paths), we
// increment the stencil buffer as we draw, preventing overlapping fragments
// from drawing. Afterwards, we need to append another draw call to clean up
// the stencil buffer (happens below in this method).
if (geometry_result.mode == GeometryResult::Mode::kPreventOverdraw) {
// the stencil buffer (happens below in this method). This can be skipped
// for draws that are fully opaque or use src blend mode.
if (geometry_result.mode == GeometryResult::Mode::kPreventOverdraw &&
options.blend_mode != BlendMode::kSource) {
options.stencil_mode =
ContentContextOptions::StencilMode::kOverdrawPreventionIncrement;
}
@ -259,7 +261,8 @@ class ColorSourceContents : public Contents {
// If we performed overdraw prevention, a subsection of the clip heightmap
// was incremented by 1 in order to self-clip. So simply append a clip
// restore to clean it up.
if (geometry_result.mode == GeometryResult::Mode::kPreventOverdraw) {
if (geometry_result.mode == GeometryResult::Mode::kPreventOverdraw &&
options.blend_mode != BlendMode::kSource) {
return RenderClipRestore(renderer, pass, entity.GetClipDepth(),
GetCoverage(entity));
}