activate method
Implementation
@override
void activate(RenderContextWebGL renderContext) {
super.activate(renderContext);
renderingContext.uniform1i(uniforms['uSampler'], 0);
renderBufferVertex.bindAttribute(attributes['aVertexPosition'], 2, 20, 0);
renderBufferVertex.bindAttribute(attributes['aVertexTextCoord'], 2, 20, 8);
renderBufferVertex.bindAttribute(attributes['aVertexAlpha'], 1, 20, 16);
}