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zill
01-25-2007, 04:45 PM
I found a function to load a PNG image, but its not working. I'm pretty sure I'm using the function properly, but whenever I load a png it is distorted with gray noise. I think the problem is with how I'm displaying the texture in my render loop, though, since everything else on the frame turns yellow when I load the image.

Here is my code:

BOOL PngLoadImage (char *fname, png_byte **ppbImageData, int *piWidth, int *piHeight, int *piChannels, png_color *pBkgColor)
{
FILE *pfFile;
png_byte pbSig[8];
int iBitDepth;
int iColorType;
double dGamma;
png_color_16 *pBackground;
png_uint_32 ulChannels;
png_uint_32 ulRowBytes;
png_byte *pbImageData = *ppbImageData;
png_byte **ppbRowPointers = NULL;
int i;
png_struct *png_ptr;
png_info *info_ptr;
png_uint_32 *pngUint32p = 0;

// open the PNG input file

if (!fname)
{
*ppbImageData = pbImageData = NULL;
return FALSE;
}

if (!(pfFile = fopen(fname, "rb")))
{
*ppbImageData = pbImageData = NULL;
return FALSE;
}

// first check the eight byte PNG signature

fread(pbSig, 1, 8, pfFile);
if (!png_check_sig(pbSig, 8))
{
*ppbImageData = pbImageData = NULL;
return FALSE;
}

// create the two png(-info) structures

png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
if (!png_ptr)
{
*ppbImageData = pbImageData = NULL;
return FALSE;
}

info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr)
{
png_destroy_read_struct(&png_ptr, NULL, NULL);
*ppbImageData = pbImageData = NULL;
return FALSE;
}

// setjmp() must be called in every function that calls a PNG-reading libpng function

if (setjmp(png_ptr->jmpbuf))
{
png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
*ppbImageData = pbImageData = NULL;
return FALSE;
}

// initialize the png structure

#if !defined(PNG_NO_STDIO)
png_init_io(png_ptr, pfFile);
#else
png_set_read_fn(png_ptr, (png_voidp)pfFile, png_read_data);
#endif

png_set_sig_bytes(png_ptr, 8);

// read all PNG info up to image data

png_read_info(png_ptr, info_ptr);

// get width, height, bit-depth and color-type

png_get_IHDR(png_ptr, info_ptr, (png_uint_32 *)piWidth, (png_uint_32 *)piHeight, &iBitDepth, &iColorType,
NULL, NULL, NULL);

// expand images of all color-type and bit-depth to 3x8 bit RGB images
// let the library process things like alpha, transparency, background

if (iBitDepth == 16)
png_set_strip_16(png_ptr);
if (iColorType == PNG_COLOR_TYPE_PALETTE)
png_set_expand(png_ptr);
if (iBitDepth < 8)
png_set_expand(png_ptr);
if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
png_set_expand(png_ptr);
if (iColorType == PNG_COLOR_TYPE_GRAY &amp;#0124;&amp;#0124;
iColorType == PNG_COLOR_TYPE_GRAY_ALPHA)
png_set_gray_to_rgb(png_ptr);

// set the background color to draw transparent and alpha images over.
if (png_get_bKGD(png_ptr, info_ptr, &amp;pBackground))
{
png_set_background(png_ptr, pBackground, PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
pBkgColor->red = (byte) pBackground->red;
pBkgColor->green = (byte) pBackground->green;
pBkgColor->blue = (byte) pBackground->blue;
}
else
{
pBkgColor = NULL;
}

// if required set gamma conversion
if (png_get_gAMA(png_ptr, info_ptr, &amp;dGamma))
png_set_gamma(png_ptr, (double) 2.2, dGamma);

// after the transformations have been registered update info_ptr data

png_read_update_info(png_ptr, info_ptr);

// get again width, height and the new bit-depth and color-type

png_get_IHDR(png_ptr, info_ptr, (png_uint_32 *)piWidth, (png_uint_32 *)piHeight, &amp;iBitDepth, &amp;iColorType,
NULL, NULL, NULL);


// row_bytes is the width x number of channels

ulRowBytes = png_get_rowbytes(png_ptr, info_ptr);
ulChannels = png_get_channels(png_ptr, info_ptr);

*piChannels = ulChannels;

// now we can allocate memory to store the image

if (pbImageData)
{
free (pbImageData);
pbImageData = NULL;
}
if ((pbImageData = (png_byte *) malloc(ulRowBytes * (*piHeight) * sizeof(png_byte))) == NULL)
{
png_destroy_read_struct(&amp;png_ptr, &amp;info_ptr, NULL);
*ppbImageData = pbImageData = NULL;
return FALSE;
}
*ppbImageData = pbImageData;

// and allocate memory for an array of row-pointers

if ((ppbRowPointers = (png_bytepp) malloc((*piHeight) * sizeof(png_bytep))) == NULL)
{
png_destroy_read_struct(&amp;png_ptr, &amp;info_ptr, NULL);
free(pbImageData);
*ppbImageData = pbImageData = NULL;
return FALSE;
}

// set the individual row-pointers to point at the correct offsets

for (i = 0; i < (*piHeight); i++)
ppbRowPointers[i] = pbImageData + i * ulRowBytes;

// now we can go ahead and just read the whole image

png_read_image(png_ptr, ppbRowPointers);

// read the additional chuncks in the PNG file (not really needed)

png_read_end(png_ptr, NULL);

// and we're done

free (ppbRowPointers);
ppbRowPointers = NULL;

// yepp, done

fclose (pfFile);

return TRUE;
}

// in main

png_byte *png;
int size = 128;
int channels = 2;
png_color col;

PngLoadImage("font1.png", &amp;png, &amp;size, &amp;size, &amp;channels, &amp;col);
if (png == NULL)
exit(0);

glGenTextures(1, &amp;texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
gluBuild2DMipmaps(GL_TEXTURE_2D, 3, size, size, GL_RGB, GL_UNSIGNED_BYTE, png);

// display callback
void ygeDraw(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture);

glBegin(GL_QUADS);
glTexCoord2d(0.0,0.0); glVertex2d(0.0,0.0);
glTexCoord2d(1.0,0.0); glVertex2d(1.0,0.0);
glTexCoord2d(1.0,1.0); glVertex2d(1.0,1.0);
glTexCoord2d(0.0,1.0); glVertex2d(0.0,1.0);
glEnd();

glutSwapBuffers();
}Can anyone help me out? Thank you for your time.

Mikkel Gjoel
01-26-2007, 02:23 AM
Sorry for not having the time to bugfix the code that you downloaded from somewhere on the internet for free and failed to get working ;) Please try one of these libraries instead - they even come with working samples that you can copy/paste from :eek:

http://freeimage.sourceforge.net/
http://openil.sourceforge.net/

Cheers,