[Feat] (MG_Backend|MG_State/ProgramState): Add default fragment shader if missing for backends requiring FS.

MobileGL/Defines.h

@@ -38,7 +38,7 @@
 #define MOBILEGL_BACKEND_TYPE_DIRECT_GLES 3
 
 // ====================== MobileGL configurations ======================= //
-#define MOBILEGL_LOG_ACTIVE_LEVEL MOBILEGL_LOG_LEVEL_FATAL
+#define MOBILEGL_LOG_ACTIVE_LEVEL MOBILEGL_LOG_LEVEL_INFO
 
 #define MOBILEGL_LOG_ENABLE_CONSOLE 0
 #define MOBILEGL_LOG_ENABLE_FILE 1

MobileGL/MG_Backend/Backends.h

@@ -24,7 +24,7 @@ namespace MobileGL {
                         .Extensions = {},               //   OpenGL Extensions
                         .IsCompatibilityProfile = false //   Is Compatibility Profile
                     },
-                .BackendCapability = {} // Backend Capability
+                .BackendCapability = {.AllowVSOnlyPrograms = false} // Backend Capability
             };
         }
 
@@ -47,7 +47,7 @@ namespace MobileGL {
                                        V_OpenGL33},
                         .IsCompatibilityProfile = false //   Is Compatibility Profile
                     },
-                .BackendCapability = {} // Backend Capability
+                .BackendCapability = {.AllowVSOnlyPrograms = false} // Backend Capability
             };
 
             inline RendererInfo RendererInfoMetal = {
@@ -63,7 +63,7 @@ namespace MobileGL {
                                        V_OpenGL33},
                         .IsCompatibilityProfile = false //   Is Compatibility Profile
                     },
-                .BackendCapability = {} // Backend Capability
+                .BackendCapability = {.AllowVSOnlyPrograms = false} // Backend Capability
             };
         } // namespace Diligent
 
@@ -81,7 +81,7 @@ namespace MobileGL {
                                        V_OpenGL33, E_GL_ARB_draw_buffers_blend},
                         .IsCompatibilityProfile = false //   Is Compatibility Profile
                     },
-                .BackendCapability = {} // Backend Capability
+                .BackendCapability = {.AllowVSOnlyPrograms = false} // Backend Capability
             };
         } // namespace DirectGLES
 

MobileGL/MG_Impl/GLImpl/Program/GL_Program.cpp

@@ -6,6 +6,7 @@
 // End of Source File Header
 
 #include "GL_Program.h"
+#include "Config.h"
 #include "MG_Util/Converters/GLToStr/GLEnumConverter.h"
 #include <MG_State/GLState/Core.h>
 #include <MG_Util/Converters/GLToMG/ProgramEnumConverter.h>
@@ -475,7 +476,7 @@ namespace MobileGL {
             auto programObject = TryToGetProgramObject(program);
             if (!programObject) return;
             MGLOG_D("%s: linking program %d", __func__, program);
-            programObject->Link();
+            programObject->Link(!MG_Config::RendererInfoPtr->BackendCapability.AllowVSOnlyPrograms);
         }
 
         void ShaderSource_State(GLuint shader, GLsizei count, const GLchar* const* string, const GLint* length) {

MobileGL/MG_State/GLState/ProgramState/ProgramObject.cpp

@@ -12,6 +12,11 @@
 #include <MG_Util/Converters/MGToGL/ProgramEnumConverter.h>
 #include <MG_Util/Converters/SPIRVCrossToGL/SpvcTypeConverter.h>
 
+const char* kDefaultFragmentShaderSource = R"(#version 460 core
+layout(location = 0) out vec4 FragColor;
+void main() {}
+)";
+
 namespace MobileGL {
     namespace MG_State {
         namespace GLState {
@@ -58,7 +63,38 @@ namespace MobileGL {
                 return count;
             }
 
-            void ProgramObject::Link() {
+            void ProgramObject::AddDefaultFragmentShaderIfMissing() {
+                Bool needsDefaultFS = false;
+                for (const auto& shader : m_shaders) {
+                    auto stage = shader->GetShaderStage();
+                    if (stage == ShaderStage::Vertex) {
+                        needsDefaultFS = true;
+                        continue;
+                    }
+                    if (stage == ShaderStage::Fragment) {
+                        needsDefaultFS = false;
+                        return;
+                    }
+                }
+
+                if (!needsDefaultFS) return;
+
+                MGLOG_D("ProgramObject %u: No fragment shader attached, adding default fragment shader.",
+                        m_externalIndex);
+                SharedPtr<ShaderObject> defaultFS = MakeShared<ShaderObject>(ShaderStage::Fragment, 0);
+                defaultFS->SetShaderSource(kDefaultFragmentShaderSource);
+                defaultFS->Compile(); // TODO: use a global default FS object.
+                auto status = defaultFS->GetCompileStatus();
+                if (!status) {
+                    MGLOG_E("ProgramObject %u: Failed to compile default fragment shader. InfoLog:\n%s",
+                            m_externalIndex, defaultFS->GetInfoLog().c_str());
+                    return;
+                }
+                m_shaders.push_back(defaultFS);
+                MGLOG_D("ProgramObject %u: Default fragment shader added.", m_externalIndex);
+            }
+
+            void ProgramObject::Link(Bool addDefaultFSIfMissingForRenderingPipelineProgram) {
                 MGLOG_D("ProgramObject %u: Link start, shaders to link: %zu", m_externalIndex, m_shaders.size());
                 // Remove detached shaders first
                 for (const auto& detachedShader : m_detachedShaders) {
@@ -69,6 +105,10 @@ namespace MobileGL {
                 Vector<GLenum> shaderTypes(m_shaders.size());
                 Vector<SharedPtr<glslang::TShader>> shaders(m_shaders.size());
 
+                if (addDefaultFSIfMissingForRenderingPipelineProgram) {
+                    AddDefaultFragmentShaderIfMissing();
+                }
+
                 for (SizeT i = 0; i < m_shaders.size(); i++) {
                     shaderTypes[i] = MG_Util::ConvertShaderStageToGLEnum(m_shaders[i]->GetShaderStage());
                     MGLOG_D("ProgramObject %u: Preparing shader[%zu] stage %s at %p", m_externalIndex, i,

MobileGL/MG_State/GLState/ProgramState/ProgramObject.h

@@ -21,7 +21,7 @@ namespace MobileGL {
                 bool AttachShader(SharedPtr<ShaderObject> shader);
                 SizeT DetachShader(SharedPtr<ShaderObject> shader);
                 SizeT RemoveShader(SharedPtr<ShaderObject> shader);
-                void Link();
+                void Link(Bool addDefaultFSIfMissingForRenderingPipelineProgram = false);
                 void MarkAsDeleted();
 
                 void SetExplicitVertexInLocation(Uint index, const char* name);
@@ -120,6 +120,7 @@ namespace MobileGL {
                 void DoReflection();
                 void GenerateBinary();
                 void WaitUntilGenerationCompleted();
+                void AddDefaultFragmentShaderIfMissing();
 
                 const Uint m_externalIndex = 0;
                 Vector<SharedPtr<ShaderObject>> m_shaders;

MobileGL/MG_Util/Types.h

@@ -248,7 +248,9 @@ namespace MobileGL {
         }
     };
 
-    struct BackendCap {};
+    struct BackendCap {
+        Bool AllowVSOnlyPrograms = false;
+    };
 
     struct GLInfo {
         Version TargetGLVersion;