Cocos2dx CCRenderTexture - OpenGL ES2 not rendered

Question

I'm trying to add a gradient to a texture in Cocos2dx 2, OpenGL ES2. But the OpenGL content is not getting rendered.

This code is based on the tutorial link: http://www.raywenderlich.com/3857/how-to-create-dynamic-textures-with-ccrendertexture

CCRenderTexture *rt = CCRenderTexture::create((int)textureSize, (int)textureSize);
rt->beginWithClear(bgColor.r, bgColor.g, bgColor.b, bgColor.a);

float gradientAlpha = 0.5;
CCPoint vertices[4];
ccColor4F colors[4];
int nVertices = 0;

vertices[nVertices] = CCPointMake(0, 0);
colors[nVertices++] = ccc4f(0, 0, 0, 0);
vertices[nVertices] = CCPointMake(textureSize, 0);
colors[nVertices++] = ccc4f(0, 0, 0, 0);
vertices[nVertices] = CCPointMake(0, textureSize);
colors[nVertices++] = ccc4f(0, 0, 0, gradientAlpha);
vertices[nVertices] = CCPointMake(textureSize, textureSize);
colors[nVertices++] = ccc4f(0, 0, 0, gradientAlpha);

// Set the shader program for OpenGL
setShaderProgram(CCShaderCache::sharedShaderCache()->programForKey(kCCShader_PositionColor));
CC_NODE_DRAW_SETUP();

glVertexAttribPointer(kCCVertexAttrib_Position, 2, GL_FLOAT, GL_FALSE, 0, vertices);
glVertexAttribPointer(kCCVertexAttrib_Color, 4, GL_FLOAT, GL_FALSE, 0, colors);
ccGLBlendFunc(CC_BLEND_SRC, CC_BLEND_DST);
glDrawArrays(GL_TRIANGLE_STRIP, 0, (GLsizei)nVertices);

CCSprite* noise = CCSprite::create("Noise.png");
ccBlendFunc blendFunc;
blendFunc.src = GL_DST_COLOR;
blendFunc.dst = GL_ZERO;
noise->setBlendFunc(blendFunc);
noise->setPosition(ccp(textureSize / 2, textureSize / 2));
noise->visit();

rt->end();
return CCSprite::createWithTexture(rt->getSprite()->getTexture());

Please let me know if I'm doing something wrong. Thank you.

Answer 1

Looks like we've to use ccVertex2F instead of CCPoint for the vertices.

Moreover, the blend function is not explicitly required for drawing the gradient.

Here is the updated C++ code:

float gradientAlpha = 0.5;
ccVertex2F vertices[4];
ccColor4F colors[4];
int nVertices = 0;

vertices[nVertices] = vertex2(0, 0);
colors[nVertices++] = ccc4f(0, 0, 0, 0);
vertices[nVertices] = vertex2(textureSize, 0);
colors[nVertices++] = ccc4f(0, 0, 0, 0);
vertices[nVertices] = vertex2(0, textureSize);
colors[nVertices++] = ccc4f(0, 0, 0, gradientAlpha);
vertices[nVertices] = vertex2(textureSize, textureSize);
colors[nVertices++] = ccc4f(0, 0, 0, gradientAlpha);

// Set the shader program for OpenGL
setShaderProgram(CCShaderCache::sharedShaderCache()->programForKey(kCCShader_PositionColor));
CC_NODE_DRAW_SETUP();

ccGLEnableVertexAttribs(kCCVertexAttribFlag_Position  | kCCVertexAttribFlag_Color);

glVertexAttribPointer(kCCVertexAttrib_Position, 2, GL_FLOAT, GL_FALSE, 0, vertices);
glVertexAttribPointer(kCCVertexAttrib_Color, 4, GL_FLOAT, GL_FALSE, 0, colors);

glDrawArrays(GL_TRIANGLE_STRIP, 0, (GLsizei)nVertices);