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mrfusion

OpenGL texture mapping problem (based on Opengl Game Programming book)

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I''m working with the first texture mapping program from the book OpenGL Game Programming (Chapter 8). It''s the one where you map a checker pattern onto a cube. The example works as long as I use the checker.bmp file that came on the CD. If I do anything - and I mean ANYTHING to the bitmap file, the program crashes when it tries to load the texture. If I open the checker.bmp file in photoshop and save it out again without touching it (as a windows bmp file), it doesn''t work. I''ve also tried loading the original file into xnview and saving it out again, the program still crashes. I get an error that says the memory could not be "read". I''m using dev-c++ to compile. Like I said the program right out of the book works and runs fine, I just can''t get it to read any other bmp files. Is this some kind of variation on the bmp format that I don''t know about? Let me know if you''d like me to upload any files if you need more information. Thanks for any help. Tom

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Are you sure that the saved file is the SAME format as the old one?
That is, same number of BPP, and the same compression type? (usually no compression).
If the loading routine is buggy, try to also use the same number of colors, if in the paletted mode.

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I''m pretty darn sure I saved it out exactly the same way.
I''ve checked their properties and as far as I can tell, they are the same. Same size, same bit depth, same compression(none).

Maybe I could upload the two images somewhere if someone wants to look at them. (Or I could zip the whole project up with the images for a more complete examination).

Tom


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Hmmm. This is not really relevant, but which version of the programming guide do you have? I have 1.2 third edition, and in this version of the source the checkered image was generated at runtime.

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I understand about makeing texture the power of 2, but my problem is that if I just open the original texture and save it out again (as the same kind of file) the program crashes.

Mongo very confused.......

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The problem is that our bitmap loading code wasn''t really robust. The problem is with this line:

bitmapImage = (unsigned char*)malloc(bitmapInfoHeader->biSizeImage);
For an uncompressed RGB image, it is valid for biSizeImage to be zero. In this case, you should use a combination of the biWidth, biHeight, and biBitcount members to determine how many bytes you really need for the bitmap. e.g.

  
// allocate enough memory for the bitmap image data

int imageSize = bitmapInfoHeader->biSizeImage;
if (imageSize == 0)
imageSize = bitmapInfoHeader->biWidth * bitmapInfoHeader->biHeight * bitmapInfoHeader->biBitCount/8;
bitmapImage = (unsigned char*)malloc(imageSize );

...
// read in the bitmap image data

fread(bitmapImage, 1, imageSize, filePtr);

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