/* -*- tab-width: 4; -*- */
/* vi: set sw=2 ts=4: */

/* $Id: b84f0063f86e9f20473d5a900eecbf1bf57b399c $ */

/*
 * Copyright 2010-2020 The Khronos Group Inc.
 * SPDX-License-Identifier: Apache-2.0
 */

/* @internal
 * @~English
 * @file
 *
 * Unpack a texture compressed with ETC1
 *
 * @author Mark Callow, HI Corporation.
 */

#include <assert.h>
#include <stdlib.h>

#include "GL/glcorearb.h"
// Not defined in glcorearb.h.
#define GL_ETC1_RGB8_OES                0x8D64
#include "ktx.h"
#include "ktxint.h"

#if SUPPORT_SOFTWARE_ETC_UNPACK
typedef unsigned int uint;
typedef unsigned char uint8;

extern void decompressBlockETC2c(uint block_part1, uint block_part2, uint8* img,
								 int width, int height, int startx, int starty, int channels);
extern void decompressBlockETC21BitAlphaC(uint block_part1, uint block_part2, uint8* img, uint8* alphaimg,
										  int width, int height, int startx, int starty, int channels);
extern void decompressBlockAlphaC(uint8* data, uint8* img,
								  int width, int height, int startx, int starty, int channels);
extern void decompressBlockAlpha16bitC(uint8* data, uint8* img,
									   int width, int height, int startx, int starty, int channels);

extern void setupAlphaTable();

// This global variable affects the behaviour of decompressBlockAlpha16bitC.
extern int formatSigned;

static void
readBigEndian4byteWord(ktx_uint32_t* pBlock, const GLubyte *s)
{
	*pBlock = (s[0] << 24) | (s[1] << 16) | (s[2] << 8) | s[3];
}


/* Unpack an ETC1_RGB8_OES format compressed texture */
extern "C" KTX_error_code
_ktxUnpackETC(const GLubyte* srcETC, const GLenum srcFormat,
			  ktx_uint32_t activeWidth, ktx_uint32_t activeHeight,
			  GLubyte** dstImage,
			  GLenum* format, GLenum* internalFormat, GLenum* type,
			  GLint R16Formats, GLboolean supportsSRGB)
{
	unsigned int width, height;
	unsigned int block_part1, block_part2;
	unsigned int x, y;
	/*const*/ GLubyte* src = (GLubyte*)srcETC;
	// AF_11BIT is used to compress R11 & RG11 though its not alpha data.
	enum {AF_NONE, AF_1BIT, AF_8BIT, AF_11BIT} alphaFormat = AF_NONE;
	int dstChannels, dstChannelBytes;

	switch (srcFormat) {
	  case GL_COMPRESSED_SIGNED_R11_EAC:
		if (R16Formats & _KTX_R16_FORMATS_SNORM) {
			dstChannelBytes = sizeof(GLshort);
			dstChannels = 1;
			formatSigned = GL_TRUE;
			*internalFormat = GL_R16_SNORM;
			*format = GL_RED;
			*type = GL_SHORT;
			alphaFormat = AF_11BIT;
		} else
			return KTX_UNSUPPORTED_TEXTURE_TYPE; 
		break;

	  case GL_COMPRESSED_R11_EAC:
		if (R16Formats & _KTX_R16_FORMATS_NORM) {
			dstChannelBytes = sizeof(GLshort);
			dstChannels = 1;
			formatSigned = GL_FALSE;
			*internalFormat = GL_R16;
			*format = GL_RED;
			*type = GL_UNSIGNED_SHORT;
			alphaFormat = AF_11BIT;
		} else
			return KTX_UNSUPPORTED_TEXTURE_TYPE; 
        break;

	  case GL_COMPRESSED_SIGNED_RG11_EAC:
		if (R16Formats & _KTX_R16_FORMATS_SNORM) {
			dstChannelBytes = sizeof(GLshort);
			dstChannels = 2;
			formatSigned = GL_TRUE;
			*internalFormat = GL_RG16_SNORM;
			*format = GL_RG;
			*type = GL_SHORT;
			alphaFormat = AF_11BIT;
		} else
			return KTX_UNSUPPORTED_TEXTURE_TYPE; 
        break;

	  case GL_COMPRESSED_RG11_EAC:
		if (R16Formats & _KTX_R16_FORMATS_NORM) {
			dstChannelBytes = sizeof(GLshort);
			dstChannels = 2;
			formatSigned = GL_FALSE;
			*internalFormat = GL_RG16;
			*format = GL_RG;
			*type = GL_UNSIGNED_SHORT;
			alphaFormat = AF_11BIT;
		} else
			return KTX_UNSUPPORTED_TEXTURE_TYPE; 
        break;

	  case GL_ETC1_RGB8_OES:
	  case GL_COMPRESSED_RGB8_ETC2:
	    dstChannelBytes = sizeof(GLubyte);
		dstChannels = 3;
		*internalFormat = GL_RGB8;
		*format = GL_RGB;
		*type = GL_UNSIGNED_BYTE;
        break;

	  case GL_COMPRESSED_RGBA8_ETC2_EAC:
	    dstChannelBytes = sizeof(GLubyte);
		dstChannels = 4;
		*internalFormat = GL_RGBA8;
		*format = GL_RGBA;
		*type = GL_UNSIGNED_BYTE;
	    alphaFormat = AF_8BIT;
		break;

	  case GL_COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2:
	    dstChannelBytes = sizeof(GLubyte);
		dstChannels = 4;
		*internalFormat = GL_RGBA8;
		*format = GL_RGBA;
		*type = GL_UNSIGNED_BYTE;
		alphaFormat = AF_1BIT;
        break;

	  case GL_COMPRESSED_SRGB8_ETC2:
		if (supportsSRGB) {
			dstChannelBytes = sizeof(GLubyte);
			dstChannels = 3;
			*internalFormat = GL_SRGB8;
			*format = GL_RGB;
			*type = GL_UNSIGNED_BYTE;
		} else
			return KTX_UNSUPPORTED_TEXTURE_TYPE; 
        break;

	  case GL_COMPRESSED_SRGB8_ALPHA8_ETC2_EAC:
		if (supportsSRGB) {
			dstChannelBytes = sizeof(GLubyte);
			dstChannels = 4;
			*internalFormat = GL_SRGB8_ALPHA8;
 			*format = GL_RGBA;
			*type = GL_UNSIGNED_BYTE;
			alphaFormat = AF_8BIT;
		} else
			return KTX_UNSUPPORTED_TEXTURE_TYPE; 
		break;

	  case GL_COMPRESSED_SRGB8_PUNCHTHROUGH_ALPHA1_ETC2:
		if (supportsSRGB) {
			dstChannelBytes = sizeof(GLubyte);
			dstChannels = 4;
			*internalFormat = GL_SRGB8_ALPHA8;
 			*format = GL_RGBA;
			*type = GL_UNSIGNED_BYTE;
			alphaFormat = AF_1BIT;
		} else
			return KTX_UNSUPPORTED_TEXTURE_TYPE; 
        break;

	  default:
	    assert(0); // Upper levels should pass only one of the above srcFormats.
        return KTX_UNSUPPORTED_TEXTURE_TYPE; // For Release configurations.
	}

    /* active_{width,height} show how many pixels contain active data,
	 * (the rest are just for making sure we have a 2*a x 4*b size).
	 */

	/* Compute the full width & height. */
	width = ((activeWidth+3)/4)*4;
	height = ((activeHeight+3)/4)*4;

	/* printf("Width = %d, Height = %d\n", width, height); */
	/* printf("active pixel area: top left %d x %d area.\n", activeWidth, activeHeight); */

	*dstImage = (GLubyte*)malloc(dstChannels*dstChannelBytes*width*height);
	if (!*dstImage) {
		return KTX_OUT_OF_MEMORY;
	}
	
	if (alphaFormat != AF_NONE)
		setupAlphaTable();

	// NOTE: none of the decompress functions actually use the <height> parameter
	if (alphaFormat == AF_11BIT) {
		// One or two 11-bit alpha channels for R or RG.
		for (y=0; y < height/4; y++) {
			for (x=0; x < width/4; x++) {
				decompressBlockAlpha16bitC(src, *dstImage, width, height, 4*x, 4*y, dstChannels);
				src += 8;
				if (srcFormat == GL_COMPRESSED_RG11_EAC || srcFormat == GL_COMPRESSED_SIGNED_RG11_EAC) {
					decompressBlockAlpha16bitC(src, *dstImage + dstChannelBytes, width, height, 4*x, 4*y, dstChannels);
					src += 8;
				}
			}
		}
	} else {
		for (y=0; y < height/4; y++) {
			for (x=0; x < width/4; x++) {
				// Decode alpha channel for RGBA
				if (alphaFormat == AF_8BIT) {
					decompressBlockAlphaC(src, *dstImage + 3, width, height, 4*x, 4*y, dstChannels);
					src += 8;
				}
				// Decode color dstChannels
				readBigEndian4byteWord(&block_part1, src);
				src += 4;
				readBigEndian4byteWord(&block_part2, src);
				src += 4;
				if (alphaFormat == AF_1BIT)
				    decompressBlockETC21BitAlphaC(block_part1, block_part2, *dstImage, 0, width, height, 4*x, 4*y, dstChannels);
				else
				    decompressBlockETC2c(block_part1, block_part2, *dstImage, width, height, 4*x, 4*y, dstChannels);
			}
		}
	}

	/* Ok, now write out the active pixels to the destination image.
	 * (But only if the active pixels differ from the total pixels)
	 */

	if( !(height == activeHeight && width == activeWidth) ) {
		int dstPixelBytes = dstChannels * dstChannelBytes;
		int dstRowBytes = dstPixelBytes * width;
		int activeRowBytes = activeWidth * dstPixelBytes;
		GLubyte *newimg = (GLubyte*)malloc(dstPixelBytes * activeWidth * activeHeight);
		unsigned int xx, yy;
		int zz;

		if (!newimg) {
			free(*dstImage);
			return KTX_OUT_OF_MEMORY;
		}
		
		/* Convert from total area to active area: */

		for (yy = 0; yy < activeHeight; yy++) {
			for (xx = 0; xx < activeWidth; xx++) {
				for (zz = 0; zz < dstPixelBytes; zz++) {
					newimg[ yy*activeRowBytes + xx*dstPixelBytes + zz ] = (*dstImage)[ yy*dstRowBytes + xx*dstPixelBytes + zz];
				}
			}
		}

		free(*dstImage);
		*dstImage = newimg;
	}

	return KTX_SUCCESS;
}

#endif /* SUPPORT_SOFTWARE_ETC_UNPACK */