Flipping OpenGL texture
- by Mk12
When I load textures from images normally, they are upside down because of OpenGL's coordinate system. What would be the best way to flip them?
glScalef(1.0f, -1.0f, 1.0f);
vertically flipping the image files manually (in Photoshop)
flipping them programatically after loading them (I don't know how)
This is the method I'm using to load png textures, in my Utilities.m file (Objective-C):
+ (GLuint)loadPngTexture:(NSString *)name {
CFURLRef textureURL = CFBundleCopyResourceURL(
CFBundleGetMainBundle(),
(CFStringRef)name,
CFSTR("png"),
CFSTR("Textures"));
NSAssert(textureURL, @"Texture name invalid");
CGImageSourceRef imageSource = CGImageSourceCreateWithURL(textureURL, NULL);
NSAssert(imageSource, @"Invalid Image Path.");
NSAssert((CGImageSourceGetCount(imageSource) > 0), @"No Image in Image Source.");
CFRelease(textureURL);
CGImageRef image = CGImageSourceCreateImageAtIndex(imageSource, 0, NULL);
NSAssert(image, @"Image not created.");
CFRelease(imageSource);
NSUInteger width = CGImageGetWidth(image);
NSUInteger height = CGImageGetHeight(image);
void *data = malloc(width * height * 4);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSAssert(colorSpace, @"Colorspace not created.");
CGContextRef context = CGBitmapContextCreate(
data,
width,
height,
8,
width * 4,
colorSpace,
kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host);
NSAssert(context, @"Context not created.");
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), image);
CGImageRelease(image);
CGContextRelease(context);
GLuint textureId;
glGenTextures(1, &textureId);
glBindTexture(GL_TEXTURE_2D, textureId);
glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP_SGIS, GL_TRUE);
glTexImage2D(
GL_TEXTURE_2D,
0,
GL_RGBA,
width,
height,
0,
GL_BGRA,
GL_UNSIGNED_INT_8_8_8_8_REV,
data);
glTexParameteri(
GL_TEXTURE_2D,
GL_TEXTURE_WRAP_S,
GL_CLAMP_TO_EDGE_SGIS);
glTexParameteri(
GL_TEXTURE_2D,
GL_TEXTURE_WRAP_T,
GL_CLAMP_TO_EDGE_SGIS);
glTexParameteri(
GL_TEXTURE_2D,
GL_TEXTURE_MAG_FILTER,
GL_LINEAR);
glTexParameteri(
GL_TEXTURE_2D,
GL_TEXTURE_MIN_FILTER,
GL_LINEAR_MIPMAP_LINEAR);
free(data);
return textureId;
}
Also, another thing I was wondering about: If I made a simple 2d game, with pixels mapped to units, would it be alright to set it up so that the origin is in the top-left corner, or would I run in to problems with other things (e.g. text rendering)?
Thanks.
