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Ataru

Problem with TGA files

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Ataru    133
Anyone have code that works to load a TGA properly. I''ve been strugling with this ever since I''ve been writing my Q3 level loader. First I loaded my TGA''s, they''re upside down. Then I flip them, the program crashes. I check to see why, seems most of the TGA files are loaded o.k, but sometimes when I print the width and the height it''s wrong. I took ne he''s TGA loading code, same thing does not flip textures, and reports invalid height sometimes (which of course causes my flipping code to crash) Anyone have a TGA loader that actually works, I''d appreciate a copy, or at least an explanation of how to fix the problem.

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rsegal    160
Forget where I got it now, but this function which I modified slightly from its original works nicely. However I am in now way trying to claim credit for it. This is not my code but it does work nicely. There''s is also a section which creates an opengl texture from the tga after it is loaded into memory. Take a few minuites to go through it, its pretty easy to understand.

It uses this header file:

--->texture.h<---
==============
#include <glut.h>

typedef struct { // Create A Structure
GLubyte *imageData; // Image Data (Up To 32 Bits)
GLuint bpp; // Image Color Depth In Bits Per Pixel
GLuint width; // Image Width
GLuint height; // Image Height
GLuint texID; // Texture ID Used To Select A Texture
} TextureImage;

bool loadTGA(TextureImage *texture, char *filename);

== End texture.h ===


--> texture.cpp <--
===============
/*
** This must be an uncompressed TGA file, make sure when
** you save it that it does this.
*/
bool loadTGA(TextureImage *texture, char *filename) {
GLubyte TGAheader[12] =
{0,0,2,0,0,0,0,0,0,0,0,0}; // Uncompressed TGA Header

GLubyte TGAcompare[12]; // Used To Compare TGA Header
GLubyte header[6]; // First 6 Useful Bytes From The Header
GLuint bytesPerPixel; // Holds Number Of Bytes Per Pixel Used In The TGA File
GLuint imageSize; // Used To Store The Image Size When Setting Aside Ram
GLuint temp; // Temporary Variable
GLuint type = GL_RGBA; // Set The Default GL Mode To RBGA (32 BPP)

FILE *file = fopen(filename, "rb"); // Open The TGA File

if (file == NULL ||
fread(TGAcompare,1,sizeof(TGAcompare),file)!=sizeof(TGAcompare) ||
memcmp(TGAheader,TGAcompare,sizeof(TGAheader))!=0
fread(header,1,sizeof(header),file)!=sizeof(header)) {

fclose(file); // If Anything Failed, Close The File
return false; // Return False
}

texture->width = header[1] * 256 + header[0];// Determine The TGA Width (highbyte*256+lowbyte)
texture->height = header[3] * 256 + header[2];
// Determine The TGA Height (highbyte*256+lowbyte)

if (texture->width <= 0 || // Is The Width Less Than Or Equal To Zero
texture->height <= 0 || // Is The Height Less Than Or Equal To Zero
(header[4]!=24 && header[4] != 32)) { // Is The TGA 24 or 32 Bit?

fclose(file);
// If Anything Failed, Close The File
return false; // Return False
}

texture->bpp = header[4];// Grab The TGA''s Bits Per Pixel (24 or 32)
bytesPerPixel = texture->bpp / 8; // Divide By 8 To Get The Bytes Per Pixel
imageSize = texture->width * texture->height * bytesPerPixel;
// Calculate The Memory Required For The TGA Data

texture->imageData=(GLubyte *)malloc(imageSize); // Reserve Memory To Hold The TGA Data

if (texture->imageData == NULL || // Does The Storage Memory Exist?
fread(texture->imageData, 1, imageSize, file) != imageSize) {
// Does The Image Size Match The Memory Reserved?

if(texture->imageData != NULL) // Was Image Data Loaded
free(texture->imageData); // If So, Release The Image Data

fclose(file); // Close The File

return false;
}

for(GLuint i = 0; i < int(imageSize); i += bytesPerPixel) { // Loop Through The Image Data // Swaps The 1st And 3rd Bytes (''R''ed and ''B''lue)
temp = texture->imageData;// Temporarily Store The Value At Image Data ''i''
texture->imageData[i] = texture->imageData[i + 2];
// Set The 1st Byte To The Value Of The 3rd Byte
texture->imageData[i + 2] = temp;// Set The 3rd Byte To The Value In ''temp'' (1st Byte Value)
}

fclose (file);
// Close The File

// Build A Texture From The Data
glGenTextures(1, &texture->texID);// Generate OpenGL texture IDs

glBindTexture(GL_TEXTURE_2D, texture->texID); // Bind Our Texture
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); // Linear Filtered
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // Linear Filtered

if (texture->bpp == 24) { // Was The TGA 24 Bits
type = GL_RGB;
// If So Set The ''type'' To GL_RGB
}

glTexImage2D(GL_TEXTURE_2D, 0, type, texture->width, texture->height, 0, type, GL_UNSIGNED_BYTE, texture->imageData);

return true; // Texture Building Went Ok, Return True
}

=== End texture.cpp ===

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Ataru    133
That''s NeHe''s source. It works fine, but not always. I think the problem is that I''m opening compressed TGA''s and this won''t handle compressed ones.

It loads the TGA''s fine, but does not properly compute the dimensions since I have a 128*256 file that the loader sees as a 256*640 file.

Photoshop opens it as 128*256 so there must be a way to get the proper dimensions. How do the people who have written Q3 loaders load their TGA''s, without getting them upside down?

Argh, I''m so frustrated.

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khirsah    122
Check the last byte (17 bytes from the beginning) of the header. If bit 4 is set, then you need to read the pixels in right-to-left order (ie. the pixels in the file are ordered beginning on the right of each row). If bit 5 is set, you need to read them in top-to-bottom order (ie. the rows of pixels in the file are ordered beginning at the top row).

Also, you can find the height and width by just reading the 16-bit values at offsets 12 and 14.

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