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OpenGL Im very confuse with Loading TGA machanism.

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There is no Loading TGA in Redbook. But I do have a killer book (Beginning OpenGL Game programming by Dave Astle). And I have reached TGA Image Loading. And I dont understand the mechanism to load TGA. Any simple steps to load uncompress and compress TGA Images?

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I don't remember what resources I used to code this (I think it might be similar to tutorials on nehe) but this is the code I use to load TGA and TGA_RLE textures.

It's pretty sloppy in general but it works.

I included the function "generateInternalTexture" but it's pretty poor design (I should not have hard coded all of those parameters for texture generation).




UINT TextureManager::LoadTGA(char *FileName)
{
int i; //counter
WORD width, height;
byte *data = NULL;
byte type, bits, length;

int rowlength, channels, filesize;
byte *pBuffer = NULL;
byte *ptr = NULL;
FILE *pFile = fopen(FileName, "rb");

if(!pFile)
{
TextureData << "TextureManager::LoadTGA: could not load tga file: " << FileName << "\n";
return NULL; //FIXME: some sort of error log or notification needed
}

fseek(pFile, 0, SEEK_END);
filesize = ftell(pFile);
fseek(pFile, 0, SEEK_SET);
pBuffer = new byte[filesize];
fread(pBuffer, 1, filesize, pFile);
fclose(pFile);

ptr = pBuffer;
length = *(byte*)ptr;
ptr+=2;

type = *(byte*)ptr;
ptr += 10;

width = *(WORD*)ptr;
ptr += sizeof(WORD);

height = *(WORD*)ptr;
ptr += sizeof(WORD);

bits = *(byte*)ptr;
ptr++;
ptr += length+1;

if(bits == 16)
{
MessageBox(NULL, "LoadTGA: Doesn't support 16bit","ERROR", MB_OK);
return NULL;
}

channels = bits / 8;
rowlength = channels * width;//length of a row in bytes
data = new byte[rowlength * height];
unsigned int y;
if(type != TGA_RLE)
{
if(channels == 3)
{
for(i = 0; i < height; i++)
{
for(y = 0; y < rowlength; y++)
{
data[(i*rowlength)+y] = *(byte*)ptr;
ptr++;
}
}
GLenum GLtype = GL_BGR_EXT;
return GenerateInternalTexture(data, channels, width, height, GLtype);
}
else
{
if(channels == 4)
{
for(i = 0; i < height; i++)
{
for(y = 0; y < rowlength; y++)
{
data[(i*rowlength)+y] = *(byte*)ptr;
ptr++;
}
}
}
GLenum GLtype = GL_BGRA_EXT;

ptr = NULL;
delete [] pBuffer;
delete ptr;

return GenerateInternalTexture(data, channels, width, height, GLtype);
}
//FIXME: make sure all of the data is cleaned up!
}
else if(type == TGA_RLE) //NOTE: LoadTGA_RLE must delete data when done!
return LoadTGA_RLE(pBuffer, ptr, bits, channels, width, height, data);
}

UINT TextureManager::LoadTGA_RLE(byte*pBuffer, byte*ptr, byte bits, byte channels, WORD width, WORD height, byte *data)
{
byte *pColor = new byte[channels];
int pixelsleft = 0;
int colorsread = 0;
int pixelsread = 0;
int totalpixels = width * height;
unsigned int y; //counter

//FIXME: must have an error logging system!
if(!ptr)
return NULL;
if(!pBuffer)
return NULL;
while(pixelsread < totalpixels)
{
pixelsleft = *(byte*)ptr;
ptr++;

if(pixelsleft < 128)
{
pixelsleft++;

if(channels == 4)
{
while(pixelsleft)
{
for(y = 0; y < channels; y++)
{
pColor[y] = *(byte*)ptr;
ptr++;
}
data[colorsread + 0] = pColor[0];
data[colorsread + 1] = pColor[1];
data[colorsread + 2] = pColor[2];
data[colorsread + 3] = pColor[3];

pixelsread++;
pixelsleft--;
colorsread += channels;
}
}
else if(channels == 3)
{
while(pixelsleft)
{
for(y = 0; y < channels; y++)
{
pColor[y] = *(byte*)ptr;
ptr++;
}
data[colorsread + 0] = pColor[0];
data[colorsread + 1] = pColor[1];
data[colorsread + 2] = pColor[2];

pixelsread++;
pixelsleft--;
colorsread += channels;
}
}
}
else
{
pixelsleft -= 127;
for(y = 0; y < channels; y++)
{
pColor[y] = *(byte*)ptr;
ptr++;
}

if(channels == 4)
{
while(pixelsleft)
{
data[colorsread + 0] = pColor[0];
data[colorsread + 1] = pColor[1];
data[colorsread + 2] = pColor[2];
data[colorsread + 3] = pColor[3];
pixelsread++;
pixelsleft--;
colorsread += channels;
}
}
else if(channels == 3)
{
while(pixelsleft)
{
data[colorsread + 0] = pColor[0];
data[colorsread + 1] = pColor[1];
data[colorsread + 2] = pColor[2];
pixelsread++;
pixelsleft--;
colorsread += channels;
}
}

}
}

ptr=NULL;
delete [] pBuffer;
delete ptr;

GLenum GLtype;
if(channels == 4)
GLtype = GL_BGRA_EXT;
if(channels == 3)
GLtype = GL_BGR_EXT;
return GenerateInternalTexture(data, channels, width, height, GLtype);
}

UINT TextureManager::GenerateInternalTexture(byte * data, int channels, int width, int height, GLenum type)
{
UINT texture;
gpNTGLAPI->ntglGenTextures(1, &texture);
gpNTGLAPI->ntglPixelStorei (GL_UNPACK_ALIGNMENT, 1);
gpNTGLAPI->ntglBindTexture(GL_TEXTURE_2D, texture);

gluBuild2DMipmaps(GL_TEXTURE_2D, channels,width,height, type, GL_UNSIGNED_BYTE, data);

gpNTGLAPI->ntglTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST); //GL_LINEAR_MIPMAP_NEAREST is faster than GL_LINEAR_MIPMAP_LINEAR
gpNTGLAPI->ntglTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_NEAREST);
gpNTGLAPI->ntglTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
return texture;
}


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I used this link to work from, plus a bunch of others from a Google of "TGA file format".

Here is my uncompressed/compressed loader code. Hopefully the comments are descriptive enough and make sense after reading the info at the link above. If not, let me know what part is unclear and I will explain it more.


// Load uncompressed image data
bool FImageTGA::LoadUncompressed()
{

// so far so good, so allocate memory for image data
// calculate byte multiplier for data array
bytesPP = spec.bpp / 8;
imageSize = spec.width * spec.height * bytesPP;
imageData = new unsigned char[imageSize];
if (imageData == NULL)
{
PrintDebug("[FImageTGA] Error: Failed to allocate %d bytes for image pixel data\n", imageSize);
return false;
}
PrintDebug("[FImageTGA] Allocated %d bytes for image pixel data\n", imageSize);

// attempt to load our image data
if (!file.read((char *)imageData, imageSize))
{
// failed, release resources
PrintDebug("[FImageTGA] ERROR: failed to read image pixel data from %s\n", filename.c_str());
delete imageData;
imageData = NULL;
return false;
}

// all ok
return true;
}

// Load compressed image data
bool FImageTGA::LoadCompressed()
{

// so far so good, so allocate memory for final image data
// calculate byte multiplier for data array
bytesPP = spec.bpp / 8;
imageSize = spec.width * spec.height * bytesPP;
imageData = new unsigned char[imageSize];
if (imageData == NULL)
{
PrintDebug("[FImageTGA] Error: Failed to allocate %d bytes for image pixel data\n", imageSize);
return false;
}
PrintDebug("[FImageTGA] Allocated %d bytes for image pixel data\n", imageSize);

// temporary variables for decoding RLE data
unsigned int numPixels = spec.width * spec.height; // number of pixels we expect to read
unsigned int pixelCount = 0; // current pixel we are dealing with
unsigned int currentByte = 0; // current byte we are dealing with
unsigned char * colorBuffer = new unsigned char[bytesPP]; // temp store for current pixel and chunk data
unsigned char * chunkByte = new unsigned char[sizeof(unsigned char)];

// keep reading a chunk and pixel data until we have accumulated
// enough pixels with the pixel count
do
{
// reset chunk byte each chunk read
chunkByte[0] = 0;

// read chunk byte
if (!file.read((char *)chunkByte, sizeof(unsigned char)))
{
PrintDebug("[FImageTGA] ERROR: Failed to read RLE chunk byte\n");
// release resources
delete colorBuffer;
delete chunkByte;
return false;
}

// check if we need to read raw or pixel data next
if(chunkByte[0] < 128)
{
// Raw data! increase chunk value by one to know how many pixels to reproduce
chunkByte[0]++;
// read in necessary number of pixels and populate the final image data array
for (int counter = 0; counter < chunkByte[0]; counter++)
{
// read pixel data
if (!file.read((char *)colorBuffer,bytesPP))
{
PrintDebug("[FImageTGA] ERROR: Failed to read necessary raw pixel data\n");
// release resources
delete colorBuffer;
delete chunkByte;
return false;
}

//transfer pixel colour to final image array
imageData[currentByte+0]=colorBuffer[0];
imageData[currentByte+1]=colorBuffer[1];
imageData[currentByte+2]=colorBuffer[2];
if (spec.bpp == 32)
imageData[currentByte+3]=colorBuffer[3];

// increase current byte to point to next spot in building our image
currentByte += bytesPP;
// increase our pixel count
pixelCount++;
}
} else {
// Pixel data! calculate how many of the following pixel we need to duplicate
chunkByte[0] -= 127;

// read pixel data
if (!file.read((char *)colorBuffer,bytesPP))
{
PrintDebug("[FImageTGA] ERROR: Failed to read necessary pixel data\n");
// release resources
delete colorBuffer;
delete chunkByte;
return false;
}
// duplicate pixel data as many times as necessary
for (int counter = 0; counter < chunkByte[0]; ++counter)
{
imageData[currentByte+0]=colorBuffer[0];
imageData[currentByte+1]=colorBuffer[1];
imageData[currentByte+2]=colorBuffer[2];
if (spec.bpp == 32)
imageData[currentByte+3]=colorBuffer[3];

// increase current byte to point to next spot
currentByte += bytesPP;
// increase our pixel count
pixelCount++;
}
}
} while (pixelCount < numPixels);
PrintDebug("[FImageTGA] Read %d pixels in agaist expected %d pixels\n",pixelCount,numPixels);

// release resources
delete colorBuffer;
delete chunkByte;

// all ok
return true;
}




hth
F451

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