Texture.m

/*
     File: Texture.m
 Abstract: n/a
  Version: 1.3
 
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#import <UIKit/UIKit.h>
#import "Texture.h"


static unsigned int nextPOT(unsigned int x)
{
	x = x - 1;
	x = x | (x >> 1);
	x = x | (x >> 2);
	x = x | (x >> 4);
	x = x | (x >> 8);
	x = x | (x >>16);
	return x + 1;
}


// This is not a fully generalized image loader. It is an example of how to use
// CGImage to directly access decompressed image data. Only the most commonly
// used image formats are supported. It will be necessary to expand this code
// to account for other uses, for example cubemaps or compressed textures.
//
// If the image format is supported, this loader will Gen a OpenGL 2D texture object
// and upload texels from it, padding to POT if needed. For image processing purposes,
// border pixels are also replicated here to ensure proper filtering during e.g. blur.
//
// The caller of this function is responsible for deleting the GL texture object.
void loadTexture(const char *name, Image *img, RendererInfo *renderer)
{
	GLuint texID = 0, components, x, y;
	GLuint imgWide, imgHigh;      // Real image size
	GLuint rowBytes, rowPixels;   // Image size padded by CGImage
	GLuint POTWide, POTHigh;      // Image size padded to next power of two
	CGBitmapInfo info;            // CGImage component layout info
	CGColorSpaceModel colormodel; // CGImage colormodel (RGB, CMYK, paletted, etc)
	GLenum internal, format;
	GLubyte *pixels, *temp = NULL;
	
	CGImageRef CGImage = [UIImage imageNamed:[NSString stringWithUTF8String:name]].CGImage;
	rt_assert(CGImage);
	if (!CGImage)
		return;
	
	// Parse CGImage info
	info       = CGImageGetBitmapInfo(CGImage);		// CGImage may return pixels in RGBA, BGRA, or ARGB order
	colormodel = CGColorSpaceGetModel(CGImageGetColorSpace(CGImage));
	size_t bpp = CGImageGetBitsPerPixel(CGImage);
	if (bpp < 8 || bpp > 32 || (colormodel != kCGColorSpaceModelMonochrome && colormodel != kCGColorSpaceModelRGB))
	{
		// This loader does not support all possible CGImage types, such as paletted images
		return;
	}
	components = (int)(bpp>>3);
	rowBytes   = (int)CGImageGetBytesPerRow(CGImage);	// CGImage may pad rows
	rowPixels  = (int)(rowBytes / components);
	imgWide    = (int)CGImageGetWidth(CGImage);
	imgHigh    = (int)CGImageGetHeight(CGImage);
	img->wide  = rowPixels;
	img->high  = imgHigh;
	img->s     = (float)imgWide / rowPixels;
	img->t     = 1.0;

	// Choose OpenGL format
	switch(bpp)
	{
		default:
			rt_assert(0 && "Unknown CGImage bpp");
		case 32:
		{
			internal = GL_RGBA;
			switch(info & kCGBitmapAlphaInfoMask)
			{
				case kCGImageAlphaPremultipliedFirst:
				case kCGImageAlphaFirst:
				case kCGImageAlphaNoneSkipFirst:
					format = GL_BGRA;
					break;
				default:
					format = GL_RGBA;
			}
			break;
		}
		case 24:
			internal = format = GL_RGB;
			break;
		case 16:
			internal = format = GL_LUMINANCE_ALPHA;
			break;
		case 8:
			internal = format = GL_LUMINANCE;
			break;
	}

	// Get a pointer to the uncompressed image data.
	//
	// This allows access to the original (possibly unpremultiplied) data, but any manipulation
	// (such as scaling) has to be done manually. Contrast this with drawing the image
	// into a CGBitmapContext, which allows scaling, but always forces premultiplication.
	CFDataRef data = CGDataProviderCopyData(CGImageGetDataProvider(CGImage));
	rt_assert(data);
	pixels = (GLubyte *)CFDataGetBytePtr(data);
	rt_assert(pixels);

	// If the CGImage component layout isn't compatible with OpenGL, fix it.
	// On the device, CGImage will generally return BGRA or RGBA.
	// On the simulator, CGImage may return ARGB, depending on the file format.
	if (format == GL_BGRA)
	{
		uint32_t *p = (uint32_t *)pixels;
		int i, num = img->wide * img->high;
		
		if ((info & kCGBitmapByteOrderMask) != kCGBitmapByteOrder32Host)
		{
			// Convert from ARGB to BGRA
			for (i = 0; i < num; i++)
				p[i] = (p[i] << 24) | ((p[i] & 0xFF00) << 8) | ((p[i] >> 8) & 0xFF00) | (p[i] >> 24);
		}
		
		// All current iPhoneOS devices support BGRA via an extension.
		if (!renderer->extension[IMG_texture_format_BGRA8888])
		{
			format = GL_RGBA;
		
			// Convert from BGRA to RGBA
			for (i = 0; i < num; i++)
				#if __LITTLE_ENDIAN__
				p[i] = ((p[i] >> 16) & 0xFF) | (p[i] & 0xFF00FF00) | ((p[i] & 0xFF) << 16);
				#else
				p[i] = ((p[i] & 0xFF00) << 16) | (p[i] & 0xFF00FF) | ((p[i] >> 16) & 0xFF00);
				#endif
		}
	}

	// Determine if we need to pad this image to a power of two.
	// There are multiple ways to deal with NPOT images on renderers that only support POT:
	// 1) scale down the image to POT size. Loses quality.
	// 2) pad up the image to POT size. Wastes memory.
	// 3) slice the image into multiple POT textures. Requires more rendering logic.
	//
	// We are only dealing with a single image here, and pick 2) for simplicity.
	//
	// If you prefer 1), you can use CoreGraphics to scale the image into a CGBitmapContext.
	POTWide = nextPOT(img->wide);
	POTHigh = nextPOT(img->high);

	if (!renderer->extension[APPLE_texture_2D_limited_npot] && (img->wide != POTWide || img->high != POTHigh))
	{
		GLuint dstBytes = POTWide * components;
		GLubyte *temp = (GLubyte *)malloc(dstBytes * POTHigh);
		
		for (y = 0; y < img->high; y++)
			memcpy(&temp[y*dstBytes], &pixels[y*rowBytes], rowBytes);
		
		img->s *= (float)img->wide/POTWide;
		img->t *= (float)img->high/POTHigh;
		img->wide = POTWide;
		img->high = POTHigh;
		pixels = temp;
		rowBytes = dstBytes;
	}

	// For filters that sample texel neighborhoods (like blur), we must replicate
	// the edge texels of the original input, to simulate CLAMP_TO_EDGE.
	{
		GLuint replicatew = MIN(MAX_FILTER_RADIUS, img->wide-imgWide);
		GLuint replicateh = MIN(MAX_FILTER_RADIUS, img->high-imgHigh);
		GLuint imgRow = imgWide * components;

		for (y = 0; y < imgHigh; y++)
			for (x = 0; x < replicatew; x++)
				memcpy(&pixels[y*rowBytes+imgRow+x*components], &pixels[y*rowBytes+imgRow-components], components);
		for (y = imgHigh; y < imgHigh+replicateh; y++)
			memcpy(&pixels[y*rowBytes], &pixels[(imgHigh-1)*rowBytes], imgRow+replicatew*components);
	}
	
	if (img->wide <= renderer->maxTextureSize && img->high <= renderer->maxTextureSize)
	{
		glGenTextures(1, &texID);
		glBindTexture(GL_TEXTURE_2D, texID);
		// Set filtering parameters appropriate for this application (image processing on screen-aligned quads.)
		// Depending on your needs, you may prefer linear filtering, or mipmap generation.
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
		glTexImage2D(GL_TEXTURE_2D, 0, internal, img->wide, img->high, 0, format, GL_UNSIGNED_BYTE, pixels);
	}
	
	if (temp) free(temp);
	CFRelease(data);
	img->texID = texID;
}