Since Open GL requires the use of "power of 2" sized images, there must be a way to use only a portion of an image as an actual texture, but I can't for the life of me figure out how. I starting playing around with glTexSubImage2D, but got no where.
I've taken the GL Sprite demo code and I'm trying to create a shape that will act as a background image. Since 320x480 is not a "power of 2" dimension, I can create a background by creating a 512x512 sized object and positioning it appropriately, but I'd rather create a 320x480 sized object and offset a 512x512 sized image within it to use as a texture. Can this be done?
Here's the code I'm working with so far:
Some setup code:
Drawing code:
I've taken the GL Sprite demo code and I'm trying to create a shape that will act as a background image. Since 320x480 is not a "power of 2" dimension, I can create a background by creating a 512x512 sized object and positioning it appropriately, but I'd rather create a 320x480 sized object and offset a 512x512 sized image within it to use as a texture. Can this be done?
Here's the code I'm working with so far:
Code:
const GLfloat spriteVertices[] = {
-1.6f, -1.6f,
1.6f, -1.6f,
-1.6f, 1.6f,
1.6f, 1.6f,
};
const GLshort spriteTexcoords[] = {
0, 0,
1, 0,
0, 1,
1, 1,
};Some setup code:
Code:
glVertexPointer(2, GL_FLOAT, 0, spriteVertices);
glEnableClientState(GL_VERTEX_ARRAY);
glTexCoordPointer(2, GL_SHORT, 0, spriteTexcoords);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
spriteImage = [UIImage imageNamed:@"BackgroundCopy.png"].CGImage;
width = CGImageGetWidth(spriteImage);
height = CGImageGetHeight(spriteImage);
if (spriteImage) {
spriteData = (GLubyte *) malloc(width * height * 4);
spriteContext = CGBitmapContextCreate(spriteData, width, height, 8, width * 4, CGImageGetColorSpace(spriteImage), kCGImageAlphaPremultipliedLast);
CGContextDrawImage(spriteContext, CGRectMake(0.0, 0.0, (CGFloat)width, (CGFloat)height), spriteImage);
CGContextRelease(spriteContext);
glGenTextures(1, &spriteTexture);
glBindTexture(GL_TEXTURE_2D, spriteTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, spriteData);
free(spriteData);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glEnable(GL_TEXTURE_2D);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_BLEND);
}Drawing code:
Code:
[EAGLContext setCurrentContext:context];
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];