[Impeller] make desktop GL render. (flutter/engine#56274)

Fixes https://github.com/flutter/flutter/issues/143387

Will be tested in https://github.com/flutter/flutter/pull/157888

engine/src/flutter/impeller/renderer/backend/gles/buffer_bindings_gles.cc

@@ -153,11 +153,17 @@ bool BufferBindingsGLES::ReadUniformsBindings(const ProcTableGLES& gl,
 
 bool BufferBindingsGLES::BindVertexAttributes(const ProcTableGLES& gl,
                                               size_t binding,
-                                              size_t vertex_offset) const {
+                                              size_t vertex_offset) {
   if (binding >= vertex_attrib_arrays_.size()) {
     return false;
   }
 
+  if (!gl.GetCapabilities()->IsES()) {
+    FML_DCHECK(vertex_array_object_ == 0);
+    gl.GenVertexArrays(1, &vertex_array_object_);
+    gl.BindVertexArray(vertex_array_object_);
+  }
+
   for (const auto& array : vertex_attrib_arrays_[binding]) {
     gl.EnableVertexAttribArray(array.index);
     gl.VertexAttribPointer(array.index,       // index
@@ -203,12 +209,16 @@ bool BufferBindingsGLES::BindUniformData(const ProcTableGLES& gl,
   return true;
 }
 
-bool BufferBindingsGLES::UnbindVertexAttributes(const ProcTableGLES& gl) const {
+bool BufferBindingsGLES::UnbindVertexAttributes(const ProcTableGLES& gl) {
   for (const auto& array : vertex_attrib_arrays_) {
     for (const auto& attribute : array) {
       gl.DisableVertexAttribArray(attribute.index);
     }
   }
+  if (!gl.GetCapabilities()->IsES()) {
+    gl.DeleteVertexArrays(1, &vertex_array_object_);
+    vertex_array_object_ = 0;
+  }
 
   return true;
 }

engine/src/flutter/impeller/renderer/backend/gles/buffer_bindings_gles.h

@@ -34,14 +34,14 @@ class BufferBindingsGLES {
 
   bool BindVertexAttributes(const ProcTableGLES& gl,
                             size_t binding,
-                            size_t vertex_offset) const;
+                            size_t vertex_offset);
 
   bool BindUniformData(const ProcTableGLES& gl,
                        Allocator& transients_allocator,
                        const Bindings& vertex_bindings,
                        const Bindings& fragment_bindings);
 
-  bool UnbindVertexAttributes(const ProcTableGLES& gl) const;
+  bool UnbindVertexAttributes(const ProcTableGLES& gl);
 
  private:
   //----------------------------------------------------------------------------
@@ -61,6 +61,7 @@ class BufferBindingsGLES {
 
   using BindingMap = std::unordered_map<std::string, std::vector<GLint>>;
   BindingMap binding_map_ = {};
+  GLuint vertex_array_object_ = 0;
 
   const std::vector<GLint>& ComputeUniformLocations(
       const ShaderMetadata* metadata);

engine/src/flutter/impeller/renderer/backend/gles/capabilities_gles.cc

@@ -124,10 +124,14 @@ CapabilitiesGLES::CapabilitiesGLES(const ProcTableGLES& gl) {
     gl.GetIntegerv(GL_MAX_SAMPLES_EXT, &value);
     supports_offscreen_msaa_ = value >= 4;
   }
-
+  is_es_ = desc->IsES();
   is_angle_ = desc->IsANGLE();
 }
 
+bool CapabilitiesGLES::IsES() const {
+  return is_es_;
+}
+
 size_t CapabilitiesGLES::GetMaxTextureUnits(ShaderStage stage) const {
   switch (stage) {
     case ShaderStage::kVertex:

engine/src/flutter/impeller/renderer/backend/gles/capabilities_gles.h

@@ -77,6 +77,9 @@ class CapabilitiesGLES final
 
   bool IsANGLE() const;
 
+  /// @brief Whether this is an ES GL variant or (if false) desktop GL.
+  bool IsES() const;
+
   // |Capabilities|
   bool SupportsOffscreenMSAA() const override;
 
@@ -133,6 +136,7 @@ class CapabilitiesGLES final
   bool supports_offscreen_msaa_ = false;
   bool supports_implicit_msaa_ = false;
   bool is_angle_ = false;
+  bool is_es_ = false;
   PixelFormat default_glyph_atlas_format_ = PixelFormat::kUnknown;
 };
 

engine/src/flutter/impeller/renderer/backend/gles/proc_table_gles.h

@@ -101,6 +101,7 @@ struct GLProc {
   PROC(BindFramebuffer);                     \
   PROC(BindRenderbuffer);                    \
   PROC(BindTexture);                         \
+  PROC(BindVertexArray);                     \
   PROC(BlendEquationSeparate);               \
   PROC(BlendFuncSeparate);                   \
   PROC(BufferData);                          \
@@ -120,6 +121,7 @@ struct GLProc {
   PROC(DeleteRenderbuffers);                 \
   PROC(DeleteShader);                        \
   PROC(DeleteTextures);                      \
+  PROC(DeleteVertexArrays);                  \
   PROC(DepthFunc);                           \
   PROC(DepthMask);                           \
   PROC(DetachShader);                        \
@@ -138,6 +140,7 @@ struct GLProc {
   PROC(GenFramebuffers);                     \
   PROC(GenRenderbuffers);                    \
   PROC(GenTextures);                         \
+  PROC(GenVertexArrays);                     \
   PROC(GetActiveUniform);                    \
   PROC(GetBooleanv);                         \
   PROC(GetFloatv);                           \