Convert an UIImage in a texture - ios

Question

In my opengl project I need to convert an UIImage in texture; what's the way to do it?
Can you help me?

Answer 1

I haven't test the following but i will decompose the conversion in 3 steps:
Extract info for your image:
UIImage* image = [UIImage imageNamed:#"imageToApplyAsATexture.png"];
CGImageRef imageRef = [image CGImage];
int width = CGImageGetWidth(imageRef);
int height = CGImageGetHeight(imageRef);
Allocate a textureData with the above properties:
GLubyte* textureData = (GLubyte *)malloc(width * height * 4); // if 4 components per pixel (RGBA)
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(textureData, width, height,
bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);
Set-up your texture:
GLuint textureID;
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glGenTextures(1, &textureID);
glBindTexture(GL_TEXTURE_2D, textureID);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData);
EDIT:
Read this tut; everything is explained from the conversion of one image to a texture and applying a texture in an iOS environment.

Answer 2

Here is swift version of getting texture out of an UIImage
func setupTexture(sourceImage: UIImage) -> GLuint {
guard let textureImage = sourceImage.cgImage else {
print("Failed to load image")
return 0
}
let width = textureImage.width
let height = textureImage.height
/*
it will write one byte each for red, green, blue, and alpha – so 4 bytes in total.
*/
let textureData = calloc(width * height * 4, MemoryLayout<GLubyte>.size) //4 components per pixel (RGBA)
let spriteContext = CGContext(data: textureData,
width: width,
height: height,
bitsPerComponent: 8,
bytesPerRow: width * 4,
space: textureImage.colorSpace!,
bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)
spriteContext?.draw(textureImage, in: CGRect(x: 0, y: 0, width: width, height: height))
var textName = GLuint()
glGenTextures(1, &textName)
glBindTexture(GLenum(GL_TEXTURE_2D), textName)
glTexParameteri(GLenum(GL_TEXTURE_2D), GLenum(GL_TEXTURE_MIN_FILTER), GL_NEAREST)
glTexImage2D(GLenum(GL_TEXTURE_2D), 0, GL_RGBA, GLsizei(width),
GLsizei(height), 0, GLenum(GL_RGBA), GLenum(GL_UNSIGNED_BYTE), textureData)
return textName
}
Note: Need to keep in mind that Core Graphics flips images when we load them in.

Answer 3

Another way of doing this using the GLKit framework:
//Path to image
NSString *path = [[NSBundle mainBundle] pathForResource:#"textureImage" ofType:#"png"];
//Set eaglContext
[EAGLContext setCurrentContext:[[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2]];
//Create texture
NSError *theError;
GLKTextureInfo *texture = [GLKTextureLoader textureWithContentsOfFile:filePath options:nil error:&theError];
glBindTexture(texture.target, texture.name);
texture.name is The OpenGL context’s name for the texture.