Implement alpha clipping for core renderers

libs_required/ACG/GL/IRenderer.cc

@@ -925,7 +925,12 @@ void IRenderer::bindObjectUniforms( ACG::RenderObject* _obj, GLSL::Program* _pro
   _prog->setUniform("g_cAmbient", _obj->ambient);
   _prog->setUniform("g_cSpecular", _obj->specular);
 
-  ACG::Vec4f materialParams(_obj->shininess, _obj->alpha, 0.0f, 0.0f);
+
+  float alphaRef = 0.f;
+  if (_obj->alphaTest && _obj->alphaFunc == GL_GREATER) {
+    alphaRef = _obj->alphaRef;
+  }
+  ACG::Vec4f materialParams(_obj->shininess, _obj->alpha, alphaRef, 0.0f);
   _prog->setUniform("g_vMaterial", materialParams);
 
   _prog->setUniform("g_cLightModelAmbient", globalLightModelAmbient_);

libs_required/ACG/GL/RenderObject.cc

@@ -189,6 +189,7 @@ void RenderObject::setMaterial( const SceneGraph::Material* _mat )
 
   // material node sets the alpha test function to GL_GREATER
   alphaFunc = GL_GREATER;
+  alphaTest = _mat->alphaTest();
   alphaRef = _mat->alphaValue();
 }
 

libs_required/ACG/GL/ShaderGenerator.cc

@@ -1073,6 +1073,7 @@ void ShaderProgGenerator::initGenDefines(ShaderGenerator* _gen)
   }
 
   _gen->addDefine("SG_ALPHA g_vMaterial.y");
+  _gen->addDefine("SG_MINALPHA g_vMaterial.z");
 
 
   _gen->addMacros(desc_.macros);
@@ -1834,6 +1835,7 @@ void ShaderProgGenerator::addFragmentBeginCode(QStringList* _code)
       (ioDesc_.passColor_ && (desc_.shadeMode == SG_SHADE_UNLIT || desc_.colorMaterialMode == GL_EMISSION)))
       _code->push_back(QString("sg_cColor = ") + ShaderGenerator::keywords.macro_inputVertexColor + QString(";"));
 
+  _code->push_back(QString("if (sg_cColor.a < SG_MINALPHA) discard;"));
   if (desc_.shadeMode == SG_SHADE_PHONG)
     addLightingCode(_code);