[Feat] (ProgramState): Implement more Global-GL-State functions.

- These functions were implemented:
  - glBlendFunc
  - glBlendFuncSeparate
  - glClear
  - glClearColor
  - glClearDepth
  - glColorMask
  - glDepthFunc
  - glDepthMask
  - glDisable
  - glEnable
  - glViewport

MG/MG_GL/State/Common/CommonState.h

@@ -10,11 +10,51 @@
 
 class CommonState {
 private:
+    // Pixel storage parameters
     std::unordered_map<GLenum, GLint> pixelStoreParams;
+
+    // Blend state
+    GLenum blendSrcRGB = GL_ONE;
+    GLenum blendDstRGB = GL_ZERO;
+    GLenum blendSrcAlpha = GL_ONE;
+    GLenum blendDstAlpha = GL_ZERO;
+    
+    // Clear state
+    GLfloat clearColor[4] = {0.0f, 0.0f, 0.0f, 0.0f};
+    GLfloat clearDepth = 1.0f;
+    
+    // Color mask
+    GLboolean colorMask[4] = {GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE};
+    
+    // Depth state
+    GLenum depthFunc = GL_LESS;
+    GLboolean depthMask = GL_TRUE;
+    
+    // Viewport
+    GLint viewport[4] = {0, 0, 0, 0};
+    
+    // Capability enables
+    std::unordered_map<GLenum, bool> capabilities;
     
 public:
+    CommonState();
+    
     // Return: the validity of the operation, according to OpenGL 3 standard
     GLenum SetPixelStoreInt(GLenum pname, GLint param);
+
+    GLenum Enable(GLenum cap);
+    GLenum Disable(GLenum cap);
+    GLenum BlendFunc(GLenum sfactor, GLenum dfactor);
+    GLenum BlendFuncSeparate(GLenum srcRGB, GLenum dstRGB,
+                             GLenum srcAlpha, GLenum dstAlpha);
+    GLenum Clear(GLbitfield mask);
+    GLenum ClearColor(GLfloat red, GLfloat green, GLfloat blue, GLfloat alpha);
+    GLenum ClearDepth(GLfloat depth);
+    GLenum ColorMask(GLboolean red, GLboolean green,
+                     GLboolean blue, GLboolean alpha);
+    GLenum DepthFunc(GLenum func);
+    GLenum DepthMask(GLboolean flag);
+    GLenum Viewport(GLint x, GLint y, GLsizei width, GLsizei height);
     
     GLint QueryPixelStoreInt(GLenum pname);
 };