[Impeller] OpenGLES: Ensure frag/vert textures are bound with unique texture units. (#47218)

The fragment shader texture bindings will smash into the texture units
used for the vertex shader bindings if the vertex and fragment shaders
both have textures.

Entities doesn't use any pipelines that tickle this case.

Author: bdero

impeller/renderer/backend/gles/buffer_bindings_gles.cc

@@ -155,11 +155,15 @@ bool BufferBindingsGLES::BindUniformData(const ProcTableGLES& gl,
     }
   }
 
-  if (!BindTextures(gl, vertex_bindings, ShaderStage::kVertex)) {
+  std::optional<size_t> next_unit_index =
+      BindTextures(gl, vertex_bindings, ShaderStage::kVertex);
+  if (!next_unit_index.has_value()) {
     return false;
   }
 
-  if (!BindTextures(gl, fragment_bindings, ShaderStage::kFragment)) {
+  if (!BindTextures(gl, fragment_bindings, ShaderStage::kFragment,
+                    *next_unit_index)
+           .has_value()) {
     return false;
   }
 
@@ -334,20 +338,22 @@ bool BufferBindingsGLES::BindUniformBuffer(const ProcTableGLES& gl,
   return true;
 }
 
-bool BufferBindingsGLES::BindTextures(const ProcTableGLES& gl,
-                                      const Bindings& bindings,
-                                      ShaderStage stage) {
-  size_t active_index = 0;
+std::optional<size_t> BufferBindingsGLES::BindTextures(
+    const ProcTableGLES& gl,
+    const Bindings& bindings,
+    ShaderStage stage,
+    size_t unit_start_index) {
+  size_t active_index = unit_start_index;
   for (const auto& data : bindings.sampled_images) {
     const auto& texture_gles = TextureGLES::Cast(*data.second.texture.resource);
     if (data.second.texture.GetMetadata() == nullptr) {
       VALIDATION_LOG << "No metadata found for texture binding.";
-      return false;
+      return std::nullopt;
     }
 
     auto location = ComputeTextureLocation(data.second.texture.GetMetadata());
     if (location == -1) {
-      return false;
+      return std::nullopt;
     }
 
     //--------------------------------------------------------------------------
@@ -356,15 +362,15 @@ bool BufferBindingsGLES::BindTextures(const ProcTableGLES& gl,
     if (active_index >= gl.GetCapabilities()->GetMaxTextureUnits(stage)) {
       VALIDATION_LOG << "Texture units specified exceed the capabilities for "
                         "this shader stage.";
-      return false;
+      return std::nullopt;
     }
     gl.ActiveTexture(GL_TEXTURE0 + active_index);
 
     //--------------------------------------------------------------------------
     /// Bind the texture.
     ///
     if (!texture_gles.Bind()) {
-      return false;
+      return std::nullopt;
     }
 
     //--------------------------------------------------------------------------
@@ -373,7 +379,7 @@ bool BufferBindingsGLES::BindTextures(const ProcTableGLES& gl,
     ///
     const auto& sampler_gles = SamplerGLES::Cast(*data.second.sampler.resource);
     if (!sampler_gles.ConfigureBoundTexture(texture_gles, gl)) {
-      return false;
+      return std::nullopt;
     }
 
     //--------------------------------------------------------------------------
@@ -386,7 +392,7 @@ bool BufferBindingsGLES::BindTextures(const ProcTableGLES& gl,
     ///
     active_index++;
   }
-  return true;
+  return active_index;
 }
 
 }  // namespace impeller

impeller/renderer/backend/gles/buffer_bindings_gles.h

@@ -70,9 +70,10 @@ class BufferBindingsGLES {
                          Allocator& transients_allocator,
                          const BufferResource& buffer);
 
-  bool BindTextures(const ProcTableGLES& gl,
-                    const Bindings& bindings,
-                    ShaderStage stage);
+  std::optional<size_t> BindTextures(const ProcTableGLES& gl,
+                                     const Bindings& bindings,
+                                     ShaderStage stage,
+                                     size_t unit_start_index = 0);
 
   BufferBindingsGLES(const BufferBindingsGLES&) = delete;