Enable use of GL_EXT_multisampled_render_to_texture extension for OpenGL backend

wgpu-hal/src/gles/adapter.rs

@@ -650,6 +650,10 @@ impl super::Adapter {
             // that's the only way to get gl_InstanceID to work correctly.
             features.set(wgt::Features::INDIRECT_FIRST_INSTANCE, supported);
         }
+        private_caps.set(
+            super::PrivateCapabilities::MULTISAMPLED_RENDER_TO_TEXTURE,
+            extensions.contains("GL_EXT_multisampled_render_to_texture"),
+        );
 
         let max_texture_size = unsafe { gl.get_parameter_i32(glow::MAX_TEXTURE_SIZE) } as u32;
         let max_texture_3d_size = unsafe { gl.get_parameter_i32(glow::MAX_3D_TEXTURE_SIZE) } as u32;

wgpu-hal/src/gles/command.rs

@@ -558,10 +558,30 @@ impl crate::CommandEncoder for super::CommandEncoder {
                 for (i, cat) in desc.color_attachments.iter().enumerate() {
                     if let Some(cat) = cat.as_ref() {
                         let attachment = glow::COLOR_ATTACHMENT0 + i as u32;
+                        // Try to use the multisampled render-to-texture extension to avoid resolving
+                        if let Some(ref rat) = cat.resolve_target {
+                            if matches!(rat.view.inner, super::TextureInner::Texture { .. })
+                                && self.private_caps.contains(
+                                    super::PrivateCapabilities::MULTISAMPLED_RENDER_TO_TEXTURE,
+                                )
+                                && !cat.ops.contains(crate::AttachmentOps::STORE)
+                                // Extension specifies that only COLOR_ATTACHMENT0 is valid
+                                && i == 0
+                            {
+                                self.cmd_buffer.commands.push(C::BindAttachment {
+                                    attachment,
+                                    view: rat.view.clone(),
+                                    depth_slice: None,
+                                    sample_count: desc.sample_count,
+                                });
+                                continue;
+                            }
+                        }
                         self.cmd_buffer.commands.push(C::BindAttachment {
                             attachment,
                             view: cat.target.view.clone(),
                             depth_slice: cat.depth_slice,
+                            sample_count: 1,
                         });
                         if let Some(ref rat) = cat.resolve_target {
                             self.state
@@ -584,6 +604,7 @@ impl crate::CommandEncoder for super::CommandEncoder {
                         attachment,
                         view: dsat.target.view.clone(),
                         depth_slice: None,
+                        sample_count: 1,
                     });
                     if aspects.contains(crate::FormatAspects::DEPTH)
                         && !dsat.depth_ops.contains(crate::AttachmentOps::STORE)

wgpu-hal/src/gles/mod.rs

@@ -232,6 +232,8 @@ bitflags::bitflags! {
         ///
         /// When this is true, instance offset emulation via vertex buffer rebinding and a shader uniform will be disabled.
         const FULLY_FEATURED_INSTANCING = 1 << 16;
+        /// Supports direct multisampled rendering to a texture without needing a resolve texture.
+        const MULTISAMPLED_RENDER_TO_TEXTURE = 1 << 17;
     }
 }
 
@@ -924,6 +926,7 @@ enum Command {
         attachment: u32,
         view: TextureView,
         depth_slice: Option<u32>,
+        sample_count: u32,
     },
     ResolveAttachment {
         attachment: u32,

wgpu-hal/src/gles/queue.rs

@@ -111,6 +111,7 @@ impl super::Queue {
         attachment: u32,
         view: &super::TextureView,
         depth_slice: Option<u32>,
+        sample_count: u32,
     ) {
         match view.inner {
             super::TextureInner::Renderbuffer { raw } => {
@@ -156,13 +157,24 @@ impl super::Queue {
                 } else {
                     unsafe {
                         assert_eq!(view.mip_levels.len(), 1);
-                        gl.framebuffer_texture_2d(
-                            fbo_target,
-                            attachment,
-                            get_2d_target(target, view.array_layers.start),
-                            Some(raw),
-                            view.mip_levels.start as i32,
-                        )
+                        if sample_count != 1 {
+                            gl.framebuffer_texture_2d_multisample(
+                                fbo_target,
+                                attachment,
+                                get_2d_target(target, view.array_layers.start),
+                                Some(raw),
+                                view.mip_levels.start as i32,
+                                sample_count as i32,
+                            )
+                        } else {
+                            gl.framebuffer_texture_2d(
+                                fbo_target,
+                                attachment,
+                                get_2d_target(target, view.array_layers.start),
+                                Some(raw),
+                                view.mip_levels.start as i32,
+                            )
+                        }
                     };
                 }
             }
@@ -1119,9 +1131,17 @@ impl super::Queue {
                 attachment,
                 ref view,
                 depth_slice,
+                sample_count,
             } => {
                 unsafe {
-                    self.set_attachment(gl, glow::DRAW_FRAMEBUFFER, attachment, view, depth_slice)
+                    self.set_attachment(
+                        gl,
+                        glow::DRAW_FRAMEBUFFER,
+                        attachment,
+                        view,
+                        depth_slice,
+                        sample_count,
+                    )
                 };
             }
             C::ResolveAttachment {
@@ -1139,6 +1159,7 @@ impl super::Queue {
                         glow::COLOR_ATTACHMENT0,
                         dst,
                         None,
+                        1,
                     )
                 };
                 unsafe {