Fix: Race condition when compute shader writes to texture. (#8527)

Author: SpeedCrash100

CHANGELOG.md

@@ -163,6 +163,10 @@ By @SupaMaggie70Incorporated in [#8206](https://github.com/gfx-rs/wgpu/pull/8206
 
 - Fixed a bug where the texture aspect was not passed through when calling `copy_texture_to_buffer` in WebGPU, causing the copy to fail for depth/stencil textures. By @Tim-Evans-Seequent in [#8445](https://github.com/gfx-rs/wgpu/pull/8445).
 
+#### GLES
+
+- Fix race when downloading texture from compute shader pass. By @SpeedCrash100 in [#8527](https://github.com/gfx-rs/wgpu/pull/8527)
+
 #### hal
 
 - `DropCallback`s are now called after dropping all other fields of their parent structs. By @jerzywilczek in [#8353](https://github.com/gfx-rs/wgpu/pull/8353)

wgpu-hal/src/gles/command.rs

@@ -311,11 +311,10 @@ impl crate::CommandEncoder for super::CommandEncoder {
         let mut combined_usage = wgt::TextureUses::empty();
         for bar in barriers {
             // GLES only synchronizes storage -> anything explicitly
-            if !bar
-                .usage
-                .from
-                .contains(wgt::TextureUses::STORAGE_READ_WRITE)
-            {
+            // if shader writes to a texture then barriers should be placed
+            if !bar.usage.from.intersects(
+                wgt::TextureUses::STORAGE_READ_WRITE | wgt::TextureUses::STORAGE_WRITE_ONLY,
+            ) {
                 continue;
             }
             // unlike buffers, there is no need for a concrete texture

wgpu-hal/src/gles/queue.rs

@@ -1257,6 +1257,10 @@ impl super::Queue {
                 }
                 unsafe { gl.memory_barrier(flags) };
             }
+            // because `STORAGE_WRITE_ONLY` and `STORAGE_READ_WRITE` are only states
+            // we can transit from due OpenGL memory barriers are used to make _subsequent_
+            // operations see changes from the _shader_ side. We filter out usage changes that are
+            // does not comes from the shader side in `transition_textures`
             C::TextureBarrier(usage) => {
                 let mut flags = 0;
                 if usage.contains(wgt::TextureUses::RESOURCE) {
@@ -1269,6 +1273,9 @@ impl super::Queue {
                 ) {
                     flags |= glow::SHADER_IMAGE_ACCESS_BARRIER_BIT;
                 }
+                if usage.intersects(wgt::TextureUses::COPY_SRC) {
+                    flags |= glow::PIXEL_BUFFER_BARRIER_BIT;
+                }
                 if usage.contains(wgt::TextureUses::COPY_DST) {
                     flags |= glow::TEXTURE_UPDATE_BARRIER_BIT;
                 }