//
// PNG Decoder
//
// written by Larry Bank
// bitbank@pobox.com
// Arduino port started 5/3/2021
// Original PNG code written 20+ years ago :)
// The goal of this code is to decode PNG images on embedded systems
//
// Copyright 2021 BitBank Software, Inc. All Rights Reserved.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//    http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//===========================================================================
//
#include "PNGdec.h"
#include "zlib.h"
#include <stdint.h>
//
// Convert 8-bit grayscale into RGB565
//
static const uint16_t usGrayTo565[] = {0x0000,0x0000,0x0000,0x0000,0x0020,0x0020,0x0020,0x0020, // 0
	0x0841,0x0841,0x0841,0x0841,0x0861,0x0861,0x0861,0x0861,
	0x1082,0x1082,0x1082,0x1082,0x10a2,0x10a2,0x10a2,0x10a2,
	0x18c3,0x18c3,0x18c3,0x18c3,0x18e3,0x18e3,0x18e3,0x18e3,
	0x2104,0x2104,0x2104,0x2104,0x2124,0x2124,0x2124,0x2124,
	0x2945,0x2945,0x2945,0x2945,0x2965,0x2965,0x2965,0x2965,
	0x3186,0x3186,0x3186,0x3186,0x31a6,0x31a6,0x31a6,0x31a6,
	0x39c7,0x39c7,0x39c7,0x39c7,0x39e7,0x39e7,0x39e7,0x39e7,
	0x4208,0x4208,0x4208,0x4208,0x4228,0x4228,0x4228,0x4228,
	0x4a49,0x4a49,0x4a49,0x4a49,0x4a69,0x4a69,0x4a69,0x4a69,
	0x528a,0x528a,0x528a,0x528a,0x52aa,0x52aa,0x52aa,0x52aa,
	0x5acb,0x5acb,0x5acb,0x5acb,0x5aeb,0x5aeb,0x5aeb,0x5aeb,
	0x630c,0x630c,0x630c,0x630c,0x632c,0x632c,0x632c,0x632c,
	0x6b4d,0x6b4d,0x6b4d,0x6b4d,0x6b6d,0x6b6d,0x6b6d,0x6b6d,
	0x738e,0x738e,0x738e,0x738e,0x73ae,0x73ae,0x73ae,0x73ae,
	0x7bcf,0x7bcf,0x7bcf,0x7bcf,0x7bef,0x7bef,0x7bef,0x7bef,
	0x8410,0x8410,0x8410,0x8410,0x8430,0x8430,0x8430,0x8430,
	0x8c51,0x8c51,0x8c51,0x8c51,0x8c71,0x8c71,0x8c71,0x8c71,
	0x9492,0x9492,0x9492,0x9492,0x94b2,0x94b2,0x94b2,0x94b2,
	0x9cd3,0x9cd3,0x9cd3,0x9cd3,0x9cf3,0x9cf3,0x9cf3,0x9cf3,
	0xa514,0xa514,0xa514,0xa514,0xa534,0xa534,0xa534,0xa534,
	0xad55,0xad55,0xad55,0xad55,0xad75,0xad75,0xad75,0xad75,
	0xb596,0xb596,0xb596,0xb596,0xb5b6,0xb5b6,0xb5b6,0xb5b6,
	0xbdd7,0xbdd7,0xbdd7,0xbdd7,0xbdf7,0xbdf7,0xbdf7,0xbdf7,
	0xc618,0xc618,0xc618,0xc618,0xc638,0xc638,0xc638,0xc638,
	0xce59,0xce59,0xce59,0xce59,0xce79,0xce79,0xce79,0xce79,
	0xd69a,0xd69a,0xd69a,0xd69a,0xd6ba,0xd6ba,0xd6ba,0xd6ba,
	0xdedb,0xdedb,0xdedb,0xdedb,0xdefb,0xdefb,0xdefb,0xdefb,
	0xe71c,0xe71c,0xe71c,0xe71c,0xe73c,0xe73c,0xe73c,0xe73c,
	0xef5d,0xef5d,0xef5d,0xef5d,0xef7d,0xef7d,0xef7d,0xef7d,
	0xf79e,0xf79e,0xf79e,0xf79e,0xf7be,0xf7be,0xf7be,0xf7be,
	0xffdf,0xffdf,0xffdf,0xffdf,0xffff,0xffff,0xffff,0xffff};

//
// C interface
//
#ifndef __cplusplus
// Forward references
PNG_STATIC int32_t readFLASH(PNGFILE *pFile, uint8_t *pBuf, int32_t iLen);
PNG_STATIC int32_t seekMem(PNGFILE *pFile, int32_t iPosition);
PNG_STATIC int PNGInit(PNGIMAGE *pPNG);

// C API
int PNG_openRAM(PNGIMAGE *pPNG, uint8_t *pData, int iDataSize, PNG_DRAW_CALLBACK *pfnDraw)
{
	pPNG->iError = PNG_SUCCESS;
	pPNG->pfnRead = readFLASH;
	pPNG->pfnSeek = seekMem;
	pPNG->pfnDraw = pfnDraw;
	pPNG->pfnOpen = NULL;
	pPNG->pfnClose = NULL;
	pPNG->PNGFile.iSize = iDataSize;
	pPNG->PNGFile.pData = pData;
	pPNG->PNGFile.iPos = 0;
	return PNGInit(pPNG);
} /* PNG_openRAM() */

#ifdef __LINUX__
int32_t readFile(PNGFILE *handle, uint8_t *buffer, int32_t length) {
	if (!handle->fHandle) return 0;
	return (int32_t)fread(buffer, 1, length, (FILE *)handle->fHandle);
}
int32_t seekFile(PNGFILE *handle, int32_t position) {
	if (!handle->fHandle) return 0;
	return fseek((FILE *)handle->fHandle, position, SEEK_SET);
}
void closeFile(void *handle) {
	if (handle) {
		FILE *f = (FILE *)handle;
		fclose(f);
	}
}
int PNG_openFile(PNGIMAGE *pPNG, const char *szFilename, PNG_DRAW_CALLBACK *pfnDraw)
{
	pPNG->iError = PNG_SUCCESS;
	pPNG->pfnRead = readFile;
	pPNG->pfnSeek = seekFile;
	pPNG->pfnDraw = pfnDraw;
	pPNG->pfnOpen = NULL;
	pPNG->pfnClose = closeFile;
	pPNG->PNGFile.fHandle = fopen(szFilename, "r+b");
	if (pPNG->PNGFile.fHandle == NULL)
		return 0;
	fseek((FILE *)pPNG->PNGFile.fHandle, 0, SEEK_END);
	pPNG->PNGFile.iSize = (int)ftell((FILE *)pPNG->PNGFile.fHandle);
	fseek((FILE *)pPNG->PNGFile.fHandle, 0, SEEK_SET);
	return PNGInit(pPNG);
} /* PNG_openFile() */
#endif // __LINUX__
void PNG_close(PNGIMAGE *pPNG)
{
	if (pPNG->pfnClose)
		(*pPNG->pfnClose)(pPNG->PNGFile.fHandle);
} /* PNG_close() */

int PNG_getWidth(PNGIMAGE *pPNG)
{
	return pPNG->iWidth;
} /* PNG_getsWidth() */

int PNG_getHeight(PNGIMAGE *pPNG)
{
	return pPNG->iHeight;
} /* PNG_getHeight() */

int PNG_getLastError(PNGIMAGE *pPNG)
{
	return pPNG->iError;
} /* PNG_getLastError() */

uint8_t *PNG_getPalette(PNGIMAGE *pPNG)
{
	return pPNG->ucPalette;
} /* PNG_getPalette() */

int PNG_getBufferSize(PNGIMAGE *pPNG)
{
	return pPNG->iHeight * pPNG->iPitch;
} /* PNG_getBufferSize() */

uint8_t * PNG_getBuffer(PNGIMAGE *pPNG)
{
	return pPNG->pImage;
} /* PNG_getBuffer() */

#endif // !__cplusplus
PNG_STATIC uint8_t PNGMakeMask(PNGDRAW *pDraw, uint8_t *pMask, uint8_t ucThreshold)
{
	uint8_t alpha, c, *s, *d, *pPal;
	uint8_t cHasOpaque = 0;
	int i, x;
	
	switch (pDraw->iPixelType) {
		case PNG_PIXEL_TRUECOLOR_ALPHA: // truecolor + alpha
		s = pDraw->pPixels;
		d = pMask;
		for (x=0; x<pDraw->iWidth; x+=8) { // groups of 8 pixels in each byte of mask
			c = 0;
			for (i=0; i<8; i++) {
				c <<= 1;
				alpha = s[3];
				if (alpha >= ucThreshold) // if opaque 'enough', set the bit
					c |= 1;
				s += 4;
			}
			*d++ = c;
			cHasOpaque |= c;
		}
		break;
	case PNG_PIXEL_GRAY_ALPHA:
		s = pDraw->pPixels;
		d = pMask;
		for (x=0; x<pDraw->iWidth; x+=8) { // groups of 8 pixels in each byte of mask
			c = 0;
			for (i=0; i<8; i++) {
				c <<= 1;
				alpha = s[1];
				if (alpha >= ucThreshold) // if opaque 'enough', set the bit
					c |= 1;
				s += 2;
			}
			*d++ = c;
			cHasOpaque |= c;
		}
		break;
	case PNG_PIXEL_INDEXED:
		s = pDraw->pPixels;
		pPal = &pDraw->pPalette[768];
		d = pMask;
		for (x=0; x<pDraw->iWidth; x+=8) { // groups of 8 pixels in each byte of mask
			uint8_t ucPix = 0;
			c = 0;
			switch (pDraw->iBpp) {
			case 2:
				for (i=0; i<8; i++) {
					if (i == 0 || i == 4)
						ucPix = *s++;
					c <<= 1;
					alpha = pPal[ucPix >> 6]; // get palette alpha for this color
					if (alpha >= ucThreshold) // if opaque 'enough', set the bit
						c |= 1;
					ucPix <<= 2;
				}
				break;
			case 4:
				for (i=0; i<8; i++) {
					if ((i & 1) == 0)
						ucPix = *s++;
					c <<= 1;
					alpha = pPal[ucPix >> 4]; // get palette alpha for this color
					if (alpha >= ucThreshold) // if opaque 'enough', set the bit
						c |= 1;
					ucPix <<= 4;
				}
				break;
			case 8:
				for (i=0; i<8; i++) {
					c <<= 1;
					alpha = pPal[s[0]]; // get palette alpha for this color
					if (alpha >= ucThreshold) // if opaque 'enough', set the bit
						c |= 1;
					s++;
				}
				break;
			} // switch on bit depth
			*d++ = c;
			cHasOpaque |= c;
		}
		break;
		default: // No alpha channel; make a mask of all 1's
		memset(pMask, 0xff, (pDraw->iWidth+7)>>3);
		cHasOpaque = 1;
		break;
	} // switch on pixel type
	return cHasOpaque; // let the caller know if any pixels are opaque
} /* PNGMakeMask() */
#ifdef ARDUINO_ESP32S3_DEV
#ifdef __cplusplus
extern "C" {
#endif // __cplusplus
	void s3_rgb565(uint8_t *pSrc, uint8_t *pDest, int iCount, bool bBigEndian);
#ifdef __cplusplus
};
#endif
#endif
//
// Convert a line of native PNG pixels into RGB565
// handles all standard pixel types
// written for simplicity, not necessarily performance
//
PNG_STATIC void PNGRGB565(PNGDRAW *pDraw, uint16_t *pPixels, int iEndiannes, uint32_t u32Bkgd, int iHasAlpha)
{
	int x, j;
	uint16_t usPixel, *pDest = pPixels;
	uint8_t c=0, a, *pPal, *s = pDraw->pPixels;
	
	switch (pDraw->iPixelType) {
	case PNG_PIXEL_GRAY_ALPHA:
		if (u32Bkgd != 0xffffffff) {
			// gray level of background color choice
			uint8_t u8BG = (uint8_t)(((u32Bkgd & 0xff) + ((u32Bkgd >> 7) & 0x1fe) + ((u32Bkgd >> 16) & 0xff)) / 4);
			uint16_t usBG = usGrayTo565[u8BG];
			for (x=0; x<pDraw->iWidth; x++) {
				c = *s++; // gray level
				a = *s++;
				if (a == 0) {
					usPixel = usBG;
				} else if (a == 255) { // fully opaque
					usPixel = usGrayTo565[c];
				} else { // mix the colors
					usPixel = (c * a) + (u8BG * (255-a));
					usPixel = usGrayTo565[(usPixel >> 8)];
				}
				if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
					usPixel = __builtin_bswap16(usPixel);
				*pDest++ = usPixel;
			} // for x
		} else {
			for (x=0; x<pDraw->iWidth; x++) {
				c = *s++; // gray level
				a = *s++;
				j = (a * c) >> 8; // multiply by the alpha
				usPixel = usGrayTo565[j];
				if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
					usPixel = __builtin_bswap16(usPixel);
				*pDest++ = usPixel;
			}
		}
		break;
	case PNG_PIXEL_GRAYSCALE:
		switch (pDraw->iBpp) {
		case 8:
			for (x=0; x<pDraw->iWidth; x++) {
				c = *s++;
				usPixel = (c >> 3); // blue
				usPixel |= ((c >> 2) << 5); // green
				usPixel |= ((c >> 3) << 11); // red
				if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
					usPixel = __builtin_bswap16(usPixel);
				*pDest++ = usPixel;
			}
			break;
		case 1:
			for (x=0; x<pDraw->iWidth; x++) {
				if ((x & 7) == 0) {
					c = *s++;
				}
				if (c & 0x80) {
					usPixel = 0xffff;
				} else {
					usPixel = 0;
				}
				*pDest++ = usPixel;
				c <<= 1;
			}
			break;
		} // switch on bpp
		break;
	case PNG_PIXEL_TRUECOLOR:
		for (x=0; x<pDraw->iWidth; x++) {
			usPixel = (s[2] >> 3); // blue
			usPixel |= ((s[1] >> 2) << 5); // green
			usPixel |= ((s[0] >> 3) << 11); // red
			if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
				usPixel = __builtin_bswap16(usPixel);
			*pDest++ = usPixel;
			s += 3;
		}
		break;
		case PNG_PIXEL_INDEXED: // palette color (can be 1/2/4 or 8 bits per pixel)
		if (pDraw->pFastPalette && !pDraw->iHasAlpha) { // faster RGB565 palette exists
			switch (pDraw->iBpp) {
			case 8:
				for (x=0; x<pDraw->iWidth; x++) {
					c = *s++;
					usPixel = pDraw->pFastPalette[c];
					if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
						usPixel = __builtin_bswap16(usPixel);
					*pDest++ = usPixel;
				}
				break;
			case 4:
				for (x=0; x<pDraw->iWidth; x+=2) {
					c = *s++;
					usPixel = pDraw->pFastPalette[c >> 4];
					if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
						usPixel = __builtin_bswap16(usPixel);
					*pDest++ = usPixel;
					usPixel = pDraw->pFastPalette[c & 0xf];
					if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
						usPixel = __builtin_bswap16(usPixel);
					*pDest++ = usPixel;
				}
				break;
			case 2:
				for (x=0; x<pDraw->iWidth; x+=4) {
					c = *s++;
					for (j=0; j<4; j++) { // work on pairs of bits
						usPixel = pDraw->pFastPalette[c >> 6];
						if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
							usPixel = __builtin_bswap16(usPixel);
						*pDest++ = usPixel;
						c <<= 2;
					}
				}
				break;
			case 1:
				for (x=0; x<pDraw->iWidth; x++) {
					if ((x & 7) == 0) {
						c = *s++;
					}
					usPixel = pDraw->pFastPalette[c >> 7];
					if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
						usPixel = __builtin_bswap16(usPixel);
					*pDest++ = usPixel;
					c <<= 1;
				}
				break;
			} // switch on bpp 
			return;
		}
		switch (pDraw->iBpp) {
			case 8: // 8-bit palette also supports palette alpha
			if (pDraw->iHasAlpha) { // use the alpha to modify the palette
				if (u32Bkgd != 0xffffffff) { // user wants to blend it with a background color
					uint32_t b_r, b_g, b_b;
					b_r = u32Bkgd & 0xff; b_g = (u32Bkgd & 0xff00) >> 8;
					b_b = (u32Bkgd >> 16) & 0xff;
					uint16_t u16Clr = (u32Bkgd & 0xf8) << 8;
					u16Clr |= ((u32Bkgd & 0xfc00) >> 5);
					u16Clr |= ((u32Bkgd & 0xf80000) >> 19);
					for (x=0; x<pDraw->iWidth; x++) {
						int a;
						c = *s++;
						a = pDraw->pPalette[768+c]; // get alpha
						if (a == 0) { // pure BGColor
							usPixel = u16Clr;
						} else if (a == 255) { // opaque
							pPal = &pDraw->pPalette[c * 3];
							usPixel = ((pPal[2] * a) >> 11); // blue
							usPixel |= (((pPal[1] * a) >> 10) << 5); // green
							usPixel |= (((pPal[0] * a) >> 11) << 11); // red
						} else { // need to mix the bg & fg colors
							
							pPal = &pDraw->pPalette[c * 3];
							usPixel = ((((pPal[2] * a) + (b_b * (255-a)))) >> 11); // blue 
							usPixel |= ((((pPal[1] * a) + (b_g * (255-a)))>> 10) << 5); // green                                
							usPixel |= ((((pPal[0] * a) + (b_r * (255-a)))>> 11) << 11); // red                                 
						} // need to mix with alpha
						if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
							usPixel = __builtin_bswap16(usPixel);
						*pDest++ = usPixel;
					} // for x
				} else { // alpha 0 = black
					for (x=0; x<pDraw->iWidth; x++) {
						int a;
						c = *s++;
						a = pDraw->pPalette[768+c]; // get alpha
						pPal = &pDraw->pPalette[c * 3];
						usPixel = ((pPal[2] * a) >> 11); // blue
						usPixel |= (((pPal[1] * a) >> 10) << 5); // green
						usPixel |= (((pPal[0] * a) >> 11) << 11); // red
						if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
							usPixel = __builtin_bswap16(usPixel);
						*pDest++ = usPixel;
					} // for x
				}
			} else {
				for (x=0; x<pDraw->iWidth; x++) {
					c = *s++;
					pPal = &pDraw->pPalette[c * 3];
					usPixel = (pPal[2] >> 3); // blue
					usPixel |= ((pPal[1] >> 2) << 5); // green
					usPixel |= ((pPal[0] >> 3) << 11); // red
					if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
						usPixel = __builtin_bswap16(usPixel);
					*pDest++ = usPixel;
				} // for x
			} // not alpha palette
			break;
		case 4:
			for (x=0; x<pDraw->iWidth; x+=2) {
				c = *s++;
				pPal = &pDraw->pPalette[(c >> 4) * 3];
				usPixel = (pPal[2] >> 3); // blue
				usPixel |= ((pPal[1] >> 2) << 5); // green
				usPixel |= ((pPal[0] >> 3) << 11); // red
				if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
					usPixel = __builtin_bswap16(usPixel);
				*pDest++ = usPixel;
				pPal = &pDraw->pPalette[(c & 0xf) * 3];
				usPixel = (pPal[2] >> 3); // blue
				usPixel |= ((pPal[1] >> 2) << 5); // green
				usPixel |= ((pPal[0] >> 3) << 11); // red
				if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
					usPixel = __builtin_bswap16(usPixel);
				*pDest++ = usPixel;
			}
			break;
		case 2:
			for (x=0; x<pDraw->iWidth; x+=4) {
				c = *s++;
				for (j=0; j<4; j++) { // work on pairs of bits
					pPal = &pDraw->pPalette[(c >> 6) * 3];
					usPixel = (pPal[2] >> 3); // blue
					usPixel |= ((pPal[1] >> 2) << 5); // green
					usPixel |= ((pPal[0] >> 3) << 11); // red
					if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
						usPixel = __builtin_bswap16(usPixel);
					*pDest++ = usPixel;
					c <<= 2;
				}
			}
			break;
		case 1:
			for (x=0; x<pDraw->iWidth; x++) {
				if ((x & 7) == 0) {
					c = *s++;
				}
				pPal = &pDraw->pPalette[(c >> 7) * 3];
				usPixel = (pPal[2] >> 3); // blue
				usPixel |= ((pPal[1] >> 2) << 5); // green
				usPixel |= ((pPal[0] >> 3) << 11); // red
				if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
					usPixel = __builtin_bswap16(usPixel);
				*pDest++ = usPixel;
				c <<= 1;
			}
			break;
		} // switch on bits per pixel
		break;
		case PNG_PIXEL_TRUECOLOR_ALPHA: // truecolor + alpha
		if (u32Bkgd != 0xffffffff) { // user wants to blend it with a background color
			uint32_t r, g, b, a;
			uint32_t b_r, b_g, b_b;
			b_r = u32Bkgd & 0xff; b_g = (u32Bkgd & 0xff00) >> 8;
			b_b = (u32Bkgd >> 16) & 0xff;
			uint16_t u16Clr = (u32Bkgd & 0xf8) << 8;
			u16Clr |= ((u32Bkgd & 0xfc00) >> 5);
			u16Clr |= ((u32Bkgd & 0xf80000) >> 19);
			for (x=0; x<pDraw->iWidth; x++) {
				r = s[0]; g = s[1]; b = s[2]; a = s[3];
				if (a == 0)
					usPixel = u16Clr;
				else if (a == 255) { // fully opaque
					usPixel = (s[2] >> 3); // blue
					usPixel |= ((s[1] >> 2) << 5); // green
					usPixel |= ((s[0] >> 3) << 11); // red
				} else { // mix the colors
					r = ((r * a) + (b_r * (255-a))) >> 8;
					g = ((g * a) + (b_g * (255-a))) >> 8;
					b = ((b * a) + (b_b * (255-a))) >> 8;
					usPixel = (b >> 3); // blue
					usPixel |= ((g >> 2) << 5); // green
					usPixel |= ((r >> 3) << 11); // red
				}
				if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
					usPixel = __builtin_bswap16(usPixel);
				*pDest++ = usPixel;
				s += 4; // skip alpha
			}
		} else { // ignore alpha
#ifdef ARDUINO_ESP32S3_DEV
			s3_rgb565(s, (uint8_t *)pDest, pDraw->iWidth, (iEndiannes == PNG_RGB565_BIG_ENDIAN));
#else
			for (x=0; x<pDraw->iWidth; x++) {
				usPixel = (s[2] >> 3); // blue
				usPixel |= ((s[1] >> 2) << 5); // green
				usPixel |= ((s[0] >> 3) << 11); // red
				if (iEndiannes == PNG_RGB565_BIG_ENDIAN)
					usPixel = __builtin_bswap16(usPixel);
				*pDest++ = usPixel;
				s += 4; // skip alpha
			}
#endif
		}
		break;
	}
} /* PNGRGB565() */
//
// Helper functions for memory based images
//
PNG_STATIC int32_t seekMem(PNGFILE *pFile, int32_t iPosition)
{
	if (iPosition < 0) iPosition = 0;
	else if (iPosition >= pFile->iSize) iPosition = pFile->iSize-1;
	pFile->iPos = iPosition;
	return iPosition;
} /* seekMem() */

PNG_STATIC int32_t readFLASH(PNGFILE *pFile, uint8_t *pBuf, int32_t iLen)
{
	int32_t iBytesRead;
	
	iBytesRead = iLen;
	if ((pFile->iSize - pFile->iPos) < iLen)
		iBytesRead = pFile->iSize - pFile->iPos;
	if (iBytesRead <= 0)
		return 0;
	memcpy_P(pBuf, &pFile->pData[pFile->iPos], iBytesRead);
	pFile->iPos += iBytesRead;
	return iBytesRead;
} /* readFLASH() */

PNG_STATIC int32_t readRAM(PNGFILE *pFile, uint8_t *pBuf, int32_t iLen)
{
	int32_t iBytesRead;
	
	iBytesRead = iLen;
	if ((pFile->iSize - pFile->iPos) < iLen)
		iBytesRead = pFile->iSize - pFile->iPos;
	if (iBytesRead <= 0)
		return 0;
	memcpy(pBuf, &pFile->pData[pFile->iPos], iBytesRead);
	pFile->iPos += iBytesRead;
	return iBytesRead;
} /* readRAM() */
//
// Verify it's a PNG file and then parse the IHDR chunk
// to get basic image size/type/etc
//
PNG_STATIC int PNGParseInfo(PNGIMAGE *pPage)
{
	uint8_t *s = pPage->ucFileBuf;
	int iBytesRead;
	
	pPage->iHasAlpha = pPage->iInterlaced = 0;
	// Read a few bytes to just parse the size/pixel info
	iBytesRead = (*pPage->pfnRead)(&pPage->PNGFile, s, 33);
	if (iBytesRead < 33) { // a PNG file this tiny? probably bad
		pPage->iError = PNG_INVALID_FILE;
		return pPage->iError;
	}
	
	if (MOTOLONG(s) != (int32_t)0x89504e47) { // check that it's a PNG file
		pPage->iError = PNG_INVALID_FILE;
		return pPage->iError;
	}
	if (MOTOLONG(&s[12]) == 0x49484452/*'IHDR'*/) {
		int len = MOTOLONG(&s[8]);
		if (len != 13) {
			pPage->iError = PNG_INVALID_FILE;
			return pPage->iError;
		}
		pPage->iWidth = MOTOLONG(&s[16]);
		pPage->iHeight = MOTOLONG(&s[20]);
		pPage->ucBpp = s[24]; // bits per pixel
		pPage->ucPixelType = s[25]; // pixel type
		pPage->iInterlaced = s[28];
		if (pPage->iInterlaced || pPage->ucBpp > 8) { // 16-bit pixels are not supported (yet)
			pPage->iError = PNG_UNSUPPORTED_FEATURE;
			return pPage->iError;
		}
		if (pPage->ucPixelType != PNG_PIXEL_GRAYSCALE && pPage->ucPixelType != PNG_PIXEL_TRUECOLOR && pPage->ucPixelType != PNG_PIXEL_INDEXED && pPage->ucPixelType != PNG_PIXEL_GRAY_ALPHA && pPage->ucPixelType != PNG_PIXEL_TRUECOLOR_ALPHA) {
			pPage->iError = PNG_INVALID_FILE;
			return pPage->iError;
		}
		if (pPage->ucBpp == 0 || pPage->ucBpp == 3 || pPage->ucBpp == 5 || pPage->ucBpp == 6) {
			pPage->iError = PNG_INVALID_FILE;
			return pPage->iError;
		}
		// calculate the number of bytes per line of pixels
		switch (pPage->ucPixelType) {
		default:
			pPage->iPitch = pPage->iWidth;
			break;
			case PNG_PIXEL_GRAYSCALE: // grayscale
			case PNG_PIXEL_INDEXED: // indexed
			pPage->iPitch = (pPage->iWidth * pPage->ucBpp + 7)/8; // bytes per pixel
			break;
			case PNG_PIXEL_TRUECOLOR: // truecolor
			pPage->iPitch = 3 * pPage->iWidth;
			break;
			case PNG_PIXEL_GRAY_ALPHA: // grayscale + alpha
			pPage->iPitch = ((2 * pPage->ucBpp) * pPage->iWidth + 7)/8;
			pPage->iHasAlpha = 1;
			break;
			case PNG_PIXEL_TRUECOLOR_ALPHA: // truecolor + alpha
			pPage->iPitch = 4 * pPage->iWidth;
			pPage->iHasAlpha = 1;
		} // switch
	}
	if (pPage->iPitch >= PNG_MAX_BUFFERED_PIXELS/2)
		return PNG_TOO_BIG;
	
	return PNG_SUCCESS;
} /* PNGParseInfo() */
//
// De-filter the current line of pixels
//
PNG_STATIC void DeFilter(uint8_t *pCurr, uint8_t *pPrev, int iWidth, int iPitch)
{
	uint8_t ucFilter = *pCurr++;
	int x, iBpp;
	if (iPitch <= iWidth)
		iBpp = 1;
	else
		iBpp = iPitch / iWidth;
	
	pPrev++; // skip filter of previous line
	switch (ucFilter) { // switch on filter type
	case PNG_FILTER_NONE:
		// nothing to do :)
		break;
	case PNG_FILTER_SUB:
		for (x=iBpp; x<iPitch; x++) {
			pCurr[x] += pCurr[x-iBpp];
		}
		break;
	case PNG_FILTER_UP:
		for (x = 0; x < iPitch; x++) {
			pCurr[x] += pPrev[x];
		}
		break;
	case PNG_FILTER_AVG:
		for (x = 0; x < iBpp; x++) {
			pCurr[x] = (pCurr[x] +
				pPrev[x] / 2 );
		}
		for (x = iBpp; x < iPitch; x++) {
			pCurr[x] = pCurr[x] +
			(pPrev[x] + pCurr[x-iBpp]) / 2;
		}
		break;
	case PNG_FILTER_PAETH:
		if (iBpp == 1) {
			int a, c;
			uint8_t *pEnd = &pCurr[iPitch];
			// First pixel/byte
			c = *pPrev++;
			a = *pCurr + c;
			*pCurr++ = (uint8_t)a;
			while (pCurr < pEnd) {
				int b, pa, pb, pc, p;
				a &= 0xff; // From previous iteration
				b = *pPrev++;
				p = b - c;
				pc = a - c;
				// assume no native ABS() instruction
				pa = p < 0 ? -p : p;
				pb = pc < 0 ? -pc : pc;
				pc = (p + pc) < 0 ? -(p + pc) : p + pc;
				// choose the best predictor
				if (pb < pa) {
					pa = pb; a = b;
				}
				if (pc < pa) a = c;
				// Calculate current pixel
				c = b;
				a += *pCurr;
				*pCurr++ = (uint8_t)a;
			}
		} else { // multi-byte
			uint8_t *pEnd = &pCurr[iBpp];
			// first pixel is treated the same as 'up'
			while (pCurr < pEnd) {
				int a = *pCurr + *pPrev++;
				*pCurr++ = (uint8_t)a;
			}
			pEnd = pEnd + (iPitch - iBpp);
			while (pCurr < pEnd) {
				int a, b, c, pa, pb, pc, p;
				c = pPrev[-iBpp];
				a = pCurr[-iBpp];
				b = *pPrev++;
				p = b - c;
				pc = a - c;
				// assume no native ABS() instruction
				pa = p < 0 ? -p : p;
				pb = pc < 0 ? -pc : pc;
				pc = (p + pc) < 0 ? -(p + pc) : p + pc;
				if (pb < pa) {
					pa = pb; a = b;
				}
				if (pc < pa) a = c;
				a += *pCurr;
				*pCurr++ = (uint8_t)a;
			}
		} // multi-byte
		break;
	} // switch on filter type
} /* DeFilter() */
//
// PNGInit
// Parse the PNG file header and confirm that it's a valid file
//
// returns 0 for success, 1 for failure
//
PNG_STATIC int PNGInit(PNGIMAGE *pPNG)
{
	return PNGParseInfo(pPNG); // gather info for image
} /* PNGInit() */
//
// Decode the PNG file
//
// You must call open() before calling decode()
// This function can be called repeatedly without having
// to close and re-open the file
//
PNG_STATIC int DecodePNG(PNGIMAGE *pPage, void *pUser, int iOptions)
{
	int err, y, iLen=0;
	int bDone, iOffset, iFileOffset, iBytesRead;
	int iMarker=0;
	uint8_t *tmp, *pCurr, *pPrev;
	z_stream d_stream; /* decompression stream */
	uint8_t *s = pPage->ucFileBuf;
	struct inflate_state *state;
	
	// Either the image buffer must be allocated or a draw callback must be set before entering
	if (pPage->pImage == NULL && pPage->pfnDraw == NULL) {
		pPage->iError = PNG_NO_BUFFER;
		return pPage->iError;
	}
	if (pPage->iPitch >= PNG_MAX_BUFFERED_PIXELS/2) {
		pPage->iError = PNG_TOO_BIG;
		return pPage->iError;
	}
	
	// Use internal buffer to maintain the current and previous lines
	y = (int)(intptr_t)&pPage->ucPixels[0];
	y &= 15; // make sure we're 16-byte aligned, -1 for filter byte
	y += (15 - y);
	pCurr = &pPage->ucPixels[y]; // so that the pixels are 16-byte aligned
	y += pPage->iPitch + 1; // both lines are 16-byte (minus 1)
	y += (15 - (y & 15));
	pPrev = &pPage->ucPixels[y];
	pPage->iError = PNG_SUCCESS;
	// Start decoding the image
	bDone = FALSE;
	// Inflate the compressed image data
	// The allocation functions are disabled and zlib has been modified
	// to not use malloc/free and instead the buffer is part of the PNG class
	d_stream.zalloc = (alloc_func)0;
	d_stream.zfree = (free_func)0;
	d_stream.opaque = (voidpf)0;
	// Insert the memory pointer here to avoid having to use malloc() inside zlib
	state = (struct inflate_state FAR *)pPage->ucZLIB;
	d_stream.state = (struct internal_state FAR *)state;
	state->window = &pPage->ucZLIB[sizeof(struct inflate_state)]; // point to 32k dictionary buffer
	err = inflateInit(&d_stream);
#ifdef FUTURE
//    if (inpage->cCompression == PIL_COMP_IPHONE_FLATE)
//        err = mz_inflateInit2(&d_stream, -15); // undocumented option which ignores header and crcs
//    else
//        err = mz_inflateInit2(&d_stream, 15);
#endif // FUTURE
	
	iFileOffset = 8; // skip PNG file signature
	iOffset = 0; // internal buffer offset starts at 0
	iBytesRead = 0; // We haven't read yet anything
	y = 0;
	d_stream.avail_out = 0;
	d_stream.next_out = pPage->pImage;
	
	// continue until fully decoded
	// parse the markers until the next data block
	while (!bDone && y < pPage->iHeight)
	{
		if (iOffset > iBytesRead-8) { // need to read more data
			iFileOffset += (iOffset - iBytesRead);
			(*pPage->pfnSeek)(&pPage->PNGFile, iFileOffset);
			iBytesRead = (*pPage->pfnRead)(&pPage->PNGFile, s, PNG_FILE_BUF_SIZE);
			if (iBytesRead < 8) {
				pPage->iError = PNG_DECODE_ERROR;
				return 1;
			}
			iFileOffset += iBytesRead;
			iOffset = 0;
		}
		
		iLen = MOTOLONG(&s[iOffset]); // chunk length
		if (iLen < 0 || iLen + (iFileOffset - iBytesRead) > pPage->PNGFile.iSize) // invalid data
		{
			pPage->iError = PNG_DECODE_ERROR;
			return 1;
		}
		iMarker = MOTOLONG(&s[iOffset+4]);
		iOffset += 8; // point to the marker data
		switch (iMarker)
		{
			case 0x44474b62: // 'bKGD' DEBUG
			break;
			case 0x67414d41: //'gAMA'
			break;
#ifdef FUTURE
			case 0x6663544C: //'fcTL' frame control block for animated PNG (need to get size of this partial image)
			pPage->iWidth = MOTOLONG(&pPage->pData[iOffset + 4]); // frame width
			pPage->iHeight = MOTOLONG(&pPage->pData[iOffset + 8]); // frame height
			bDone = TRUE;
			break;
#endif
			case 0x504c5445: //'PLTE' palette colors
			memset(&pPage->ucPalette[768], 0xff, 256); // assume all colors are opaque unless specified
			memcpy(pPage->ucPalette, &s[iOffset], iLen);
			if (iOptions & PNG_FAST_PALETTE) { // create a RGB565 palette
				int i, iColors = 1 << pPage->ucBpp;
				uint16_t usPixel, *d;
				uint8_t *s = pPage->ucPalette;
				d = (uint16_t *)&pPage->ucPixels[sizeof(pPage->ucPixels)-512];
				for (i=0; i<iColors; i++) {
					usPixel = (s[2] >> 3); // blue
					usPixel |= ((s[1] >> 2) << 5); // green
					usPixel |= ((s[0] >> 3) << 11); // red
					*d++ = usPixel;
					s += 3;
				}
			}
			break;
			case 0x74524e53: //'tRNS' transparency info
			if (pPage->ucPixelType == PNG_PIXEL_INDEXED) // if palette exists
			{
				memcpy(&pPage->ucPalette[768], &s[iOffset], iLen);
				pPage->iHasAlpha = 1;
			}
			else if (iLen == 2) // for grayscale images
			{
				pPage->iTransparent = s[iOffset + 1]; // lower part of 2-byte value is transparent color index
				pPage->iHasAlpha = 1;
			}
			else if (iLen == 6) // transparent color for 24-bpp image
			{
				pPage->iTransparent = s[iOffset + 5]; // lower part of 2-byte value is transparent color value
				pPage->iTransparent |= (s[iOffset + 3] << 8);
				pPage->iTransparent |= (s[iOffset + 1] << 16);
				pPage->iHasAlpha = 1;
			}
			break;
			case 0x49444154: //'IDAT' image data block
			while (iLen) {
				if (iOffset >= iBytesRead) {
					// we ran out of data; get some more
					iBytesRead = (*pPage->pfnRead)(&pPage->PNGFile, pPage->ucFileBuf, (iLen > PNG_FILE_BUF_SIZE) ? PNG_FILE_BUF_SIZE : iLen);
					iFileOffset += iBytesRead;
					iOffset = 0;
				} else {
					// number of bytes remaining in buffer
					iBytesRead -= iOffset;
				}
				if (iBytesRead > iLen) { // we read too much
					d_stream.next_in  = &pPage->ucFileBuf[iOffset];
					d_stream.avail_in = iLen;
					iOffset += iLen; // point to start of next marker
					iBytesRead -= iLen; // keep remaining byte count
					iLen = 0; // every byte will be decoded
				} else {
					d_stream.next_in  = &pPage->ucFileBuf[iOffset];
					d_stream.avail_in = iBytesRead;
					iLen -= iBytesRead;
					iOffset += iBytesRead;
					iBytesRead = 0;
				}
				//        if (iMarker == 0x66644154) // data starts at offset 4 in APNG frame data block
				//        {
				//            d_stream.next_in += 4;
				//            d_stream.avail_in -= 4;
				//        }
				err = 0;
				while (err == Z_OK) {
					if (d_stream.avail_out == 0) { // reset for next line
						d_stream.avail_out = pPage->iPitch+1;
						d_stream.next_out = pCurr;
					} // otherwise it could be a continuation of an unfinished line
					err = inflate(&d_stream, Z_NO_FLUSH, 0);
					if ((err == Z_OK || err == Z_STREAM_END) && d_stream.avail_out == 0) {// successfully decoded line
						DeFilter(pCurr, pPrev, pPage->iWidth, pPage->iPitch);
						if (pPage->pImage == NULL) { // no image buffer, send it line by line
							PNGDRAW pngd;
							pngd.pUser = pUser;
							pngd.iPitch = pPage->iPitch;
							pngd.iWidth = pPage->iWidth;
							pngd.pPalette = pPage->ucPalette;
							pngd.pFastPalette = (iOptions & PNG_FAST_PALETTE) ? (uint16_t *)&pPage->ucPixels[sizeof(pPage->ucPixels)-512] : NULL;
							pngd.pPixels = pCurr+1;
							pngd.iPixelType = pPage->ucPixelType;
							pngd.iHasAlpha = pPage->iHasAlpha;
							pngd.iBpp = pPage->ucBpp;
							pngd.y = y;
							(*pPage->pfnDraw)(&pngd);
						} else {
							// copy to destination bitmap
							memcpy(&pPage->pImage[y * pPage->iPitch], &pCurr[1], pPage->iPitch);
						}
						y++;
						// swap current and previous lines
						tmp = pCurr; pCurr = pPrev; pPrev = tmp;
					} else { // some error
						tmp = NULL;
					}
				}
				if (err == Z_STREAM_END && d_stream.avail_out == 0) {
					// successful decode, stop here
					y = pPage->iHeight;
					bDone = TRUE;
				} else  if (err == Z_DATA_ERROR || err == Z_STREAM_ERROR) {
					iLen = 0; // quit now
					y = pPage->iHeight;
					pPage->iError = PNG_DECODE_ERROR;
					bDone = TRUE; // force loop to exit with error
				} else if (err == Z_BUF_ERROR) {
					y |= 0; // need more data
				}
			} // while (iLen)
			if (iBytesRead) { // data remaining in buffer
				// Restore iBytesRead to be total ucFileBuf bytes, not remainder
				iBytesRead += iOffset;
			} else {
				// We consumed everything, so move the pointer to the zero.
				// We haven't read CRC for the block, but it doesn't matter as
				// pfnSeek will move past it to the next chunk.
				iOffset = 0;
			}
			break;
			//               case 0x69545874: //'iTXt'
			//               case 0x7a545874: //'zTXt'
#ifdef FUTURE
			case 0x74455874: //'tEXt'
			{
				char szTemp[256];
				char *pDest = NULL;
				memcpy(szTemp, &s[iOffset], 80); // get the label length (Title, Author, Description, Copyright, Creation Time, Software, Disclaimer, Warning, Source, Comment)
				i = (int)strlen(szTemp) + 1; // start of actual text
				if (strcmp(szTemp, "Comment") == 0 || strcmp(szTemp, "Description") == 0) pDest = &pPage->szComment[0];
				else if (strcmp(szTemp, "Software") == 0) pDest = &pPage->szSoftware[0];
				else if (strcmp(szTemp, "Author") == 0) pDest = &pPage->szArtist[0];
				if (pDest != NULL)
				{
					if ((iLen - i) < 128)
					{
						memcpy(pPage->szComment, &pPage->pData[iOffset + i], iLen - i);
						pPage->szComment[iLen - i + 1] = 0;
					}
					else
					{
						memcpy(pPage->szComment, &pPage->pData[iOffset + i], 127);
						pPage->szComment[127] = '\0';
					}
				}
			}
			break;
#endif
		} // switch
		iOffset += (iLen + 4); // skip data + CRC
	} // while y < height
	err = inflateEnd(&d_stream);
	return pPage->iError;
} /* DecodePNG() */

