OpenGL: Support blend equation

src/video_core/renderer_opengl/gl_rasterizer.cpp

@@ -937,6 +937,8 @@ void RasterizerOpenGL::SyncBlendEnabled() {
 
 void RasterizerOpenGL::SyncBlendFuncs() {
     const auto& regs = Pica::g_state.regs;
+    state.blend.rgb_equation = PicaToGL::BlendEquation(regs.output_merger.alpha_blending.blend_equation_rgb);
+    state.blend.a_equation = PicaToGL::BlendEquation(regs.output_merger.alpha_blending.blend_equation_a);
     state.blend.src_rgb_func = PicaToGL::BlendFunc(regs.output_merger.alpha_blending.factor_source_rgb);
     state.blend.dst_rgb_func = PicaToGL::BlendFunc(regs.output_merger.alpha_blending.factor_dest_rgb);
     state.blend.src_a_func = PicaToGL::BlendFunc(regs.output_merger.alpha_blending.factor_source_a);

src/video_core/renderer_opengl/gl_state.cpp

@@ -36,6 +36,8 @@ OpenGLState::OpenGLState() {
     stencil.action_stencil_fail = GL_KEEP;
 
     blend.enabled = false;
+    blend.rgb_equation = GL_FUNC_ADD;
+    blend.a_equation = GL_FUNC_ADD;
     blend.src_rgb_func = GL_ONE;
     blend.dst_rgb_func = GL_ZERO;
     blend.src_a_func = GL_ONE;
@@ -165,6 +167,11 @@ void OpenGLState::Apply() const {
                             blend.src_a_func, blend.dst_a_func);
     }
 
+    if (blend.rgb_equation != cur_state.blend.rgb_equation ||
+            blend.a_equation != cur_state.blend.a_equation) {
+        glBlendEquationSeparate(blend.rgb_equation, blend.a_equation);
+    }
+
     if (logic_op != cur_state.logic_op) {
         glLogicOp(logic_op);
     }

src/video_core/renderer_opengl/gl_state.h

@@ -40,6 +40,8 @@ public:
 
     struct {
         bool enabled; // GL_BLEND
+        GLenum rgb_equation; // GL_BLEND_EQUATION_RGB
+        GLenum a_equation; // GL_BLEND_EQUATION_ALPHA
         GLenum src_rgb_func; // GL_BLEND_SRC_RGB
         GLenum dst_rgb_func; // GL_BLEND_DST_RGB
         GLenum src_a_func; // GL_BLEND_SRC_ALPHA

src/video_core/renderer_opengl/pica_to_gl.h

@@ -78,6 +78,26 @@ inline GLenum WrapMode(Pica::Regs::TextureConfig::WrapMode mode) {
     return gl_mode;
 }
 
+inline GLenum BlendEquation(Pica::Regs::BlendEquation equation) {
+    static const GLenum blend_equation_table[] = {
+        GL_FUNC_ADD,              // BlendEquation::Add
+        GL_FUNC_SUBTRACT,         // BlendEquation::Subtract
+        GL_FUNC_REVERSE_SUBTRACT, // BlendEquation::ReverseSubtract
+        GL_MIN,                   // BlendEquation::Min
+        GL_MAX,                   // BlendEquation::Max
+    };
+
+    // Range check table for input
+    if (static_cast<size_t>(equation) >= ARRAY_SIZE(blend_equation_table)) {
+        LOG_CRITICAL(Render_OpenGL, "Unknown blend equation %d", equation);
+        UNREACHABLE();
+
+        return GL_FUNC_ADD;
+    }
+
+    return blend_equation_table[(unsigned)equation];
+}
+
 inline GLenum BlendFunc(Pica::Regs::BlendFactor factor) {
     static const GLenum blend_func_table[] = {
         GL_ZERO,                     // BlendFactor::Zero