understanding OpenGL ES crash causes and ways to debug one - c++

Question

Leaning how to use OpenGL ES under cocos2d-x.
Help me to understand while the below function crashes with EXC_BAD_ACCESS on noise->visit(); which probably means that my OpenGL state is screwed-up by the time the command is executed.
My method:
Sprite* GameLevelLayer::spriteWithColor(Color4F bgColor, float textureWidth, float textureHeight)
{
// 1: Create new RenderTexture
auto rt = RenderTexture::create(textureWidth, textureHeight);
// 2: Call RenderTexture:begin
rt->beginWithClear(bgColor.r, bgColor.g, bgColor.b, bgColor.a);
// 3: Draw into the texture
//// gradient
gradient_command.init(rt->getGlobalZOrder());
gradient_command.func = std::bind(&GameLevelLayer::onDrawGradient, this, textureWidth, textureHeight);
auto renderer = Director::getInstance()->getRenderer();
renderer->addCommand(&gradient_command);
//// noise cloud
BlendFunc blendFunc;
blendFunc.src = GL_DST_COLOR;
blendFunc.dst = GL_ZERO;
auto noise = Sprite::create("Noise.png");
noise->setBlendFunc(blendFunc);
noise->setPosition(Vec2(textureWidth / 2, textureHeight / 2));
// XXX
noise->visit();
// 4: Call RenderTexture:end
rt->end();
// 5: Create a new Sprite from the texture
return Sprite::createWithTexture(rt->getSprite()->getTexture());
}
and the gradient:
void GameLevelLayer::onDrawGradient(float textureWidth, float textureHeight)
{
setGLProgram(ShaderCache::getInstance()->getGLProgram(GLProgram::SHADER_NAME_POSITION_COLOR));
getGLProgram()->use();
getGLProgram()->setUniformsForBuiltins();
float gradientAlpha = 0.8f;
std::vector<Vec2> vertices;
std::vector<Color4F> colors;
vertices.push_back(Vec2(0, 0));
colors.push_back(Color4F(0.0f, 0.0f, 0.0f, 0.0f ));
vertices.push_back(Vec2(textureWidth, 0));
colors.push_back(Color4F(0.0f, 0.0f, 0.0f, 0.0f ));
vertices.push_back(Vec2(0, textureHeight));
colors.push_back(Color4F(0.0f, 0.0f, 0.0f, gradientAlpha ));
vertices.push_back(Vec2(textureWidth, textureHeight));
colors.push_back(Color4F(0.0f, 0.0f, 0.0f, gradientAlpha ));
GL::enableVertexAttribs(GL::VERTEX_ATTRIB_FLAG_POSITION | GL::VERTEX_ATTRIB_FLAG_COLOR);
glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_POSITION, 2, GL_FLOAT, GL_FALSE, 0, vertices.data());
glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_COLOR, 4, GL_FLOAT, GL_FALSE, 0, colors.data());
glBlendFunc(CC_BLEND_SRC, CC_BLEND_DST);
glDrawArrays(GL_TRIANGLE_STRIP, 0, (GLsizei)vertices.size());
}
Is this because I am using parameters of a wrong size, somewhere? How does one go about debugging something like this?