Rendering Texture Quad to Screen or FBO (OpenGL ES)

Question

I need to render the texture on the iOS device's screen or a render-to-texture frame buffer object. But it does not show any texture. It's all black.

(I am loading texture with image myself for testing purpose)

//Load texture data

UIImage *image=[UIImage imageNamed:@"textureImage.png"];

    GLuint width = FRAME_WIDTH;
    GLuint height = FRAME_HEIGHT;

    //Create context
    void *imageData = malloc(height * width * 4);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(imageData, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    CGColorSpaceRelease(colorSpace);

    //Prepare image
    CGContextClearRect(context, CGRectMake(0, 0, width, height));
    CGContextDrawImage(context, CGRectMake(0, 0, width, height), image.CGImage);

    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

Simple Texture Quad drawing code mentioned here

//Bind Texture, Bind render-to-texture FBO and then draw the quad

const float quadPositions[] = {  1.0,  1.0, 0.0, 
                                -1.0,  1.0, 0.0, 
                                -1.0, -1.0, 0.0, 
                                -1.0, -1.0, 0.0, 
                                 1.0, -1.0, 0.0, 
                                 1.0,  1.0, 0.0 };
const float quadTexcoords[] = { 1.0, 1.0, 
                                0.0, 1.0, 
                                0.0, 0.0, 
                                0.0, 0.0, 
                                1.0, 0.0, 
                                1.0, 1.0 };

// stop using VBO
glBindBuffer(GL_ARRAY_BUFFER, 0);

// setup buffer offsets
glVertexAttribPointer(ATTRIB_VERTEX, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), quadPositions);
glVertexAttribPointer(ATTRIB_TEXCOORD0, 2, GL_FLOAT, GL_FALSE, 2*sizeof(float), quadTexcoords);

// ensure the proper arrays are enabled
glEnableVertexAttribArray(ATTRIB_VERTEX);
glEnableVertexAttribArray(ATTRIB_TEXCOORD0);

//Bind Texture and render-to-texture FBO.
glBindTexture(GL_TEXTURE_2D, GLid);

//Actually wanted to render it to render-to-texture FBO, but now testing directly on default FBO.
//glBindFramebuffer(GL_FRAMEBUFFER, textureFBO[pixelBuffernum]);

// draw
glDrawArrays(GL_TRIANGLES, 0, 2*3);

What am I doing wrong in this code?

P.S. I'm not familiar with shaders yet, so it is difficult for me to make use of them right now.

Answer 1

glDrawArrays(GL_TRIANGLES, 0, 2*3) won't draw anything because you do not have any shaders attached. OpenGL ES 2 does not have a fixed pipeline, therefore you need to implement your own shaders. You can use GLKit's GLKBaseEffect as a shader or better write you own.

I recommend you the following series of tutorials as a starting point: http://iphonedevelopment.blogspot.com/2010/11/opengl-es-20-for-ios-chapter-4.html