add premultiplied alpha blend mode (#2342)

src/raylib.h

@@ -839,6 +839,7 @@ typedef enum {
     BLEND_MULTIPLIED,               // Blend textures multiplying colors
     BLEND_ADD_COLORS,               // Blend textures adding colors (alternative)
     BLEND_SUBTRACT_COLORS,          // Blend textures subtracting colors (alternative)
+    BLEND_ALPHA_PREMUL,             // Blend premultiplied textures considering alpha
     BLEND_CUSTOM                    // Blend textures using custom src/dst factors (use rlSetBlendMode())
 } BlendMode;
 

src/rlgl.h

@@ -433,6 +433,7 @@ typedef enum {
     RL_BLEND_MULTIPLIED,               // Blend textures multiplying colors
     RL_BLEND_ADD_COLORS,               // Blend textures adding colors (alternative)
     RL_BLEND_SUBTRACT_COLORS,          // Blend textures subtracting colors (alternative)
+    RL_BLEND_ALPHA_PREMUL,             // Blend premultiplied textures considering alpha
     RL_BLEND_CUSTOM                    // Blend textures using custom src/dst factors (use rlSetBlendFactors())
 } rlBlendMode;
 
@@ -1778,10 +1779,11 @@ void rlSetBlendMode(int mode)
             case RL_BLEND_MULTIPLIED: glBlendFunc(GL_DST_COLOR, GL_ONE_MINUS_SRC_ALPHA); glBlendEquation(GL_FUNC_ADD); break;
             case RL_BLEND_ADD_COLORS: glBlendFunc(GL_ONE, GL_ONE); glBlendEquation(GL_FUNC_ADD); break;
             case RL_BLEND_SUBTRACT_COLORS: glBlendFunc(GL_ONE, GL_ONE); glBlendEquation(GL_FUNC_SUBTRACT); break;
-            case RL_BLEND_CUSTOM: 
+            case RL_BLEND_ALPHA_PREMUL: glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA); glBlendEquation(GL_FUNC_ADD); break;
+            case RL_BLEND_CUSTOM:
             {
                 // NOTE: Using GL blend src/dst factors and GL equation configured with rlSetBlendFactors()
-                glBlendFunc(RLGL.State.glBlendSrcFactor, RLGL.State.glBlendDstFactor); glBlendEquation(RLGL.State.glBlendEquation); 
+                glBlendFunc(RLGL.State.glBlendSrcFactor, RLGL.State.glBlendDstFactor); glBlendEquation(RLGL.State.glBlendEquation);
             } break;
             default: break;
         }
@@ -3911,7 +3913,7 @@ void rlComputeShaderDispatch(unsigned int groupX, unsigned int groupY, unsigned
 unsigned int rlLoadShaderBuffer(unsigned long long size, const void *data, int usageHint)
 {
     unsigned int ssbo = 0;
-    
+
 #if defined(GRAPHICS_API_OPENGL_43)
     glGenBuffers(1, &ssbo);
     glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
@@ -3944,7 +3946,7 @@ void rlUpdateShaderBufferElements(unsigned int id, const void *data, unsigned lo
 unsigned long long rlGetShaderBufferSize(unsigned int id)
 {
     long long size = 0;
-    
+
 #if defined(GRAPHICS_API_OPENGL_43)
     glBindBuffer(GL_SHADER_STORAGE_BUFFER, id);
     glGetInteger64v(GL_SHADER_STORAGE_BUFFER_SIZE, &size);