How to use multiple textures in OpenGL ES 2.0 - iphone

Question

I would like to set up a texture array to use for my shape. I have researched this topic on the internet but there are hardly any references a newbie like me can make use of.
Again, what I am trying to achieve, is a texture array that I can use to map different textures onto the different faces of my shape.
As of now I have got only one texture that I generate from a UIView.
My core questions are:
How do I set up this array ?
How do I load textures into that array ?
How do I use this array ?
Here is my code:
- (void)setupGL {
[EAGLContext setCurrentContext:self.myContext];
self.effect = [[GLKBaseEffect alloc] init];
self.layer.contentsScale = 2.0;
BOOL useTexture = YES;
// Create default framebuffer object.
glGenFramebuffers(1, &defaultFrameBuffer);
glBindFramebuffer(GL_FRAMEBUFFER, defaultFrameBuffer);
myView = [[MyView alloc]initWithFrame:CGRectMake(0,0,320,320)];
self.effect.transform.projectionMatrix = GLKMatrix4MakePerspective(45.0f,0.9f, 0.01f, .08f);
self.effect.transform.projectionMatrix = GLKMatrix4Translate(self.effect.transform.projectionMatrix, 0, 0.1, 1.2);
rotMatrix = GLKMatrix4Translate(self.effect.transform.modelviewMatrix,0,0,-2);
self.effect.transform.modelviewMatrix = rotMatrix;
/*********************
MAPPING UIVIEW ONTO THE FACE
****************/
CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
self.effect.texture2d0.enabled = true;
GLubyte *pixelBuffer = (GLubyte *)malloc(
4 *
myView.bounds.size.width * coordToPixScale *
myView.bounds.size.height * coordToPixScale);
CGContextRef context =
CGBitmapContextCreate(pixelBuffer,
myView.bounds.size.width*coordToPixScale, myView.bounds.size.height*coordToPixScale,
8, 4*myView.bounds.size.width *coordToPixScale,
colourSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colourSpace);
// draw the view to the buffer
[myView.layer renderInContext:context];
// upload to OpenGL
glTexImage2D(GL_TEXTURE_2D, 0,
GL_RGBA,
myView.bounds.size.width * coordToPixScale, myView.bounds.size.height * coordToPixScale, 0,
GL_RGBA, GL_UNSIGNED_BYTE, pixelBuffer);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
// clean up
CGContextRelease(context);
glGenBuffers(1, &texArray);
glBindBuffer(GL_ARRAY_BUFFER, texArray);
glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
glBufferData(GL_ARRAY_BUFFER, sizeof(TexCoords), TexCoords, GL_STATIC_DRAW);
glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, 0,0);
/**************************
******************************************/
free(pixelBuffer);
glGenRenderbuffers(1, &depthBuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthBuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, myView.bounds.size.width * coordToPixScale, myView.bounds.size.height * coordToPixScale);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthBuffer);
glEnable(GL_DEPTH_TEST);
glGenBuffers(1, &vertexArray);
glBindBuffer(GL_ARRAY_BUFFER, vertexArray);
glEnableVertexAttribArray(GLKVertexAttribPosition);
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);
glVertexAttribPointer(GLKVertexAttribPosition,3,GL_FLOAT,GL_FALSE,0,0);
}
This method is called when it gets drawn:
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect {
self.opaque = NO;
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
[self.effect prepareToDraw];
glDrawArrays(GL_TRIANGLES, 0, sizeof(Vertices) / (sizeof(GLfloat) * 3));
}

Answer 1

Seeing as you are using GLKit I think you can load the textures more easily. First create your CGImageRef:
CGImageRef image0 =
[[UIImage imageNamed:#"image0.png"] CGImage];
Load that into a GLKTextureInfo ivar textureInfo0 as follows:
self.textureInfo0 = [GLKTextureLoader
textureWithCGImage:image1
options:[NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES],
GLKTextureLoaderOriginBottomLeft, nil]
error:NULL];
Do exactly the same with your second texture. That should be named textureInfo1.
Loading the texture coords is done with glEnableVertexAttribArray and glVertexAttribPointer using the GLKVertexAttribTexCoord0 attribute. I think you have that set up above. You will need to map the coordinates from your texture to the target triangles. For example, if you wanted to draw a square - which composes of two triangles - you would need to map the S and T coordinates of the source image twice, i.e. for each respective triangle. For example triangle 1 with coords:
{0.0f, 0.0f}, {1.0f, 0.0f}, {0.0f, 1.0f}.
(if you plot that you will see it is a triangle)
Then, the second triangle of the square would be as follows:
{1.0f, 0.0f}, {0.0f, 1.0f}, {1.0f, 1.0f}.
Next, in your drawing method;
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
first, set up the initial texture:
self.effect.texture2d0.name = self.textureInfo0.name;
self.effect.texture2d0.target = self.textureInfo0.target;
[self.effect prepareToDraw];
Draw your triangles as need be with glDrawArrays. Then, replace with the second texture:
self.effect.texture2d0.name = self.textureInfo1.name;
self.effect.texture2d0.target = self.textureInfo1.target;
[self.effect prepareToDraw];
and draw the rest of the triangles with glDrawArrays. They will use the second texture.
Continue replacing self.effect.texture2d0.name and self.effect.texture2d0.target with different GLKTextureInfo instances to draw the different textures.