[Impeller] split downsample shader into GLES variant. (#56376)

This fixes a crash reported on a moto g4 where the on device shader compiler fails to process the ifdef.

ci/licenses_golden/licenses_flutter

@@ -43065,6 +43065,7 @@ ORIGIN: ../../../flutter/impeller/entity/shaders/blending/porter_duff_blend.vert
 ORIGIN: ../../../flutter/impeller/entity/shaders/blending/vertices_uber.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/clip.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/clip.vert + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/entity/shaders/downsample.glsl + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/filters/border_mask_blur.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/filters/color_matrix_color_filter.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/filters/filter_position.vert + ../../../flutter/LICENSE
@@ -43093,6 +43094,7 @@ ORIGIN: ../../../flutter/impeller/entity/shaders/runtime_effect.vert + ../../../
 ORIGIN: ../../../flutter/impeller/entity/shaders/solid_fill.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/solid_fill.vert + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/texture_downsample.frag + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/entity/shaders/texture_downsample_gles.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/texture_fill.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/texture_fill.vert + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/texture_fill_strict_src.frag + ../../../flutter/LICENSE
@@ -45925,6 +45927,7 @@ FILE: ../../../flutter/impeller/entity/shaders/blending/porter_duff_blend.vert
 FILE: ../../../flutter/impeller/entity/shaders/blending/vertices_uber.frag
 FILE: ../../../flutter/impeller/entity/shaders/clip.frag
 FILE: ../../../flutter/impeller/entity/shaders/clip.vert
+FILE: ../../../flutter/impeller/entity/shaders/downsample.glsl
 FILE: ../../../flutter/impeller/entity/shaders/filters/border_mask_blur.frag
 FILE: ../../../flutter/impeller/entity/shaders/filters/color_matrix_color_filter.frag
 FILE: ../../../flutter/impeller/entity/shaders/filters/filter_position.vert
@@ -45953,6 +45956,7 @@ FILE: ../../../flutter/impeller/entity/shaders/runtime_effect.vert
 FILE: ../../../flutter/impeller/entity/shaders/solid_fill.frag
 FILE: ../../../flutter/impeller/entity/shaders/solid_fill.vert
 FILE: ../../../flutter/impeller/entity/shaders/texture_downsample.frag
+FILE: ../../../flutter/impeller/entity/shaders/texture_downsample_gles.frag
 FILE: ../../../flutter/impeller/entity/shaders/texture_fill.frag
 FILE: ../../../flutter/impeller/entity/shaders/texture_fill.vert
 FILE: ../../../flutter/impeller/entity/shaders/texture_fill_strict_src.frag

impeller/entity/BUILD.gn

@@ -51,6 +51,7 @@ impeller_shaders("entity_shaders") {
     "shaders/gradients/fast_gradient.vert",
     "shaders/gradients/fast_gradient.frag",
     "shaders/texture_downsample.frag",
+    "shaders/texture_downsample_gles.frag",
   ]
 }
 

impeller/entity/contents/content_context.cc

@@ -336,8 +336,8 @@ ContentContext::ContentContext(
     clip_pipelines_.SetDefault(
         options,
         std::make_unique<ClipPipeline>(*context_, clip_pipeline_descriptor));
-    texture_downsample_pipelines_.CreateDefault(
-        *context_, options_trianglestrip, {supports_decal});
+    texture_downsample_pipelines_.CreateDefault(*context_,
+                                                options_trianglestrip);
     rrect_blur_pipelines_.CreateDefault(*context_, options_trianglestrip);
     texture_strict_src_pipelines_.CreateDefault(*context_, options);
     tiled_texture_pipelines_.CreateDefault(*context_, options,
@@ -454,10 +454,14 @@ ContentContext::ContentContext(
                                                  options_trianglestrip);
   yuv_to_rgb_filter_pipelines_.CreateDefault(*context_, options_trianglestrip);
 
-  // GLES only shader that is unsupported on macOS.
-#if defined(IMPELLER_ENABLE_OPENGLES) && !defined(FML_OS_MACOSX)
+#if defined(IMPELLER_ENABLE_OPENGLES)
   if (GetContext()->GetBackendType() == Context::BackendType::kOpenGLES) {
+#if !defined(FML_OS_MACOSX)
+    // GLES only shader that is unsupported on macOS.
     tiled_texture_external_pipelines_.CreateDefault(*context_, options);
+#endif  // !defined(FML_OS_MACOSX)
+    texture_downsample_gles_pipelines_.CreateDefault(*context_,
+                                                     options_trianglestrip);
   }
 #endif  // IMPELLER_ENABLE_OPENGLES
 

impeller/entity/contents/content_context.h

@@ -70,6 +70,7 @@
 #include "impeller/entity/vertices_uber.frag.h"
 
 #ifdef IMPELLER_ENABLE_OPENGLES
+#include "impeller/entity/texture_downsample_gles.frag.h"
 #include "impeller/entity/tiled_texture_fill_external.frag.h"
 #endif  // IMPELLER_ENABLE_OPENGLES
 
@@ -239,6 +240,9 @@ using VerticesUberShader = RenderPipelineHandle<PorterDuffBlendVertexShader,
 using TiledTextureExternalPipeline =
     RenderPipelineHandle<TextureFillVertexShader,
                          TiledTextureFillExternalFragmentShader>;
+using TextureDownsampleGlesPipeline =
+    RenderPipelineHandle<TextureFillVertexShader,
+                         TextureDownsampleGlesFragmentShader>;
 #endif  // IMPELLER_ENABLE_OPENGLES
 
 /// Pipeline state configuration.
@@ -426,6 +430,11 @@ class ContentContext {
   }
 
 #ifdef IMPELLER_ENABLE_OPENGLES
+  std::shared_ptr<Pipeline<PipelineDescriptor>>
+  GetDownsampleTextureGlesPipeline(ContentContextOptions opts) const {
+    return GetPipeline(texture_downsample_gles_pipelines_, opts);
+  }
+
   std::shared_ptr<Pipeline<PipelineDescriptor>> GetTiledTextureExternalPipeline(
       ContentContextOptions opts) const {
     FML_DCHECK(GetContext()->GetBackendType() ==
@@ -873,6 +882,8 @@ class ContentContext {
 #ifdef IMPELLER_ENABLE_OPENGLES
   mutable Variants<TiledTextureExternalPipeline>
       tiled_texture_external_pipelines_;
+  mutable Variants<TextureDownsampleGlesPipeline>
+      texture_downsample_gles_pipelines_;
 #endif  // IMPELLER_ENABLE_OPENGLES
   mutable Variants<TiledTexturePipeline> tiled_texture_pipelines_;
   mutable Variants<GaussianBlurPipeline> gaussian_blur_pipelines_;

impeller/entity/contents/filters/gaussian_blur_filter_contents.cc

@@ -396,7 +396,20 @@ fml::StatusOr<RenderTarget> MakeDownsampleSubpass(
           pass.SetCommandLabel("Gaussian blur downsample");
           auto pipeline_options = OptionsFromPass(pass);
           pipeline_options.primitive_type = PrimitiveType::kTriangleStrip;
+#ifdef IMPELLER_ENABLE_OPENGLES
+          // The GLES backend conditionally supports decal tile mode, while
+          // decal is always supported for Vulkan and Metal.
+          if (renderer.GetDeviceCapabilities()
+                  .SupportsDecalSamplerAddressMode() ||
+              tile_mode != Entity::TileMode::kDecal) {
+            pass.SetPipeline(renderer.GetDownsamplePipeline(pipeline_options));
+          } else {
+            pass.SetPipeline(
+                renderer.GetDownsampleTextureGlesPipeline(pipeline_options));
+          }
+#else
           pass.SetPipeline(renderer.GetDownsamplePipeline(pipeline_options));
+#endif  // IMPELLER_ENABLE_OPENGLES
 
           TextureFillVertexShader::FrameInfo frame_info;
           frame_info.mvp = Matrix::MakeOrthographic(ISize(1, 1));
@@ -407,8 +420,6 @@ fml::StatusOr<RenderTarget> MakeDownsampleSubpass(
           frag_info.edge = edge;
           frag_info.ratio = ratio;
           frag_info.pixel_size = Vector2(1.0f / Size(input_texture->GetSize()));
-          frag_info.use_decal =
-              (tile_mode == Entity::TileMode::kDecal) ? 1.0 : 0.0;
 
           const Quad& uvs = pass_args.uvs;
           std::array<VS::PerVertexData, 4> vertices = {

impeller/entity/shaders/downsample.glsl

@@ -0,0 +1,44 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+precision mediump float;
+
+#include <impeller/constants.glsl>
+#include <impeller/types.glsl>
+
+uniform f16sampler2D texture_sampler;
+
+uniform FragInfo {
+  float edge;
+  float ratio;
+  vec2 pixel_size;
+}
+frag_info;
+
+in highp vec2 v_texture_coords;
+
+out vec4 frag_color;
+
+vec4 Sample(vec2 uv) {
+#ifdef SUPPORTS_DECAL
+  return texture(texture_sampler, uv, float16_t(kDefaultMipBias));
+#else
+  if ((uv.x < 0 || uv.y < 0 || uv.x > 1 || uv.y > 1)) {
+    return vec4(0);
+  } else {
+    return texture(texture_sampler, uv, float16_t(kDefaultMipBias));
+  }
+#endif
+}
+
+void main() {
+  vec4 total = vec4(0.0);
+  for (float i = -frag_info.edge; i <= frag_info.edge; i += 2) {
+    for (float j = -frag_info.edge; j <= frag_info.edge; j += 2) {
+      total += (Sample(v_texture_coords + frag_info.pixel_size * vec2(i, j)) *
+                frag_info.ratio);
+    }
+  }
+  frag_color = total;
+}

impeller/entity/shaders/texture_downsample.frag

@@ -2,47 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-precision mediump float;
+#define SUPPORTS_DECAL 1
 
-#include <impeller/constants.glsl>
-#include <impeller/types.glsl>
-
-layout(constant_id = 0) const float supports_decal = 1.0;
-
-uniform f16sampler2D texture_sampler;
-
-uniform FragInfo {
-  float edge;
-  float ratio;
-  float use_decal;
-  vec2 pixel_size;
-}
-frag_info;
-
-in highp vec2 v_texture_coords;
-
-out vec4 frag_color;
-
-vec4 Sample(vec2 uv) {
-  if (supports_decal == 1.0) {
-    return texture(texture_sampler, uv, float16_t(kDefaultMipBias));
-  } else {
-    if (frag_info.use_decal == 1.0 &&
-        (uv.x < 0 || uv.y < 0 || uv.x > 1 || uv.y > 1)) {
-      return vec4(0);
-    } else {
-      return texture(texture_sampler, uv, float16_t(kDefaultMipBias));
-    }
-  }
-}
-
-void main() {
-  vec4 total = vec4(0.0);
-  for (float i = -frag_info.edge; i <= frag_info.edge; i += 2) {
-    for (float j = -frag_info.edge; j <= frag_info.edge; j += 2) {
-      total += (Sample(v_texture_coords + frag_info.pixel_size * vec2(i, j)) *
-                frag_info.ratio);
-    }
-  }
-  frag_color = total;
-}
+#include <downsample.glsl>

impeller/entity/shaders/texture_downsample_gles.frag

@@ -0,0 +1,5 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <downsample.glsl>