BMP file problem

Shawn Andrews · 2013-01-03T05:50:58

My opengl program loads BMP's like such: //Makes the image into a texture, and returns the id of the texture GLuint loadTexture(Image* image) { GLuint textureId; glGenTextures(1, &textureId); //Make room for our texture glBindTexture(GL_TEXTURE_2D, textureId); //Tell OpenGL which texture to edit //Map the image to the texture glTexImage2D(GL_TEXTURE_2D, //Always GL_TEXTURE_2D 0, //0 for now GL_RGB, //Format OpenGL uses for image image->width, image->height, //Width and height 0, //The border of the image GL_RGB, //GL_RGB, because pixels are stored in RGB format GL_UNSIGNED_BYTE, //GL_UNSIGNED_BYTE, because pixels are stored //as unsigned numbers image->pixels); //The actual pixel data return textureId; //Returns the id of the texture } with assistance from the imageloader.cpp&.h files: //imageloader.cpp #include <assert.h> #include <fstream> #include "imageloader.h" using namespace std; Image::Image( char* ps, int w, int h) : pixels(ps), width(w), height(h) { } Image::~Image() { delete[] pixels; } namespace { //Converts a four-character array to an integer, using little-endian form int toInt(const char* bytes) { return (int)(((unsigned char)bytes[3] << 24) | (( unsigned char)bytes[2] << 16) | (( unsigned char)bytes[1] << 8) | ( unsigned char)bytes[0]); } //Converts a two-character array to a short, using little-endian form short toShort(const char* bytes) { return (short)(((unsigned char)bytes[1] << 8) | ( unsigned char)bytes[0]); } //Reads the next four bytes as an integer, using little-endian form int readInt(ifstream &input) { char buffer[4]; input.read(buffer, 4); return toInt(buffer); } //Reads the next two bytes as a short, using little-endian form short readShort(ifstream &input) { char buffer[2]; input.read(buffer, 2); return toShort(buffer); } //Just like auto_ptr, but for arrays template<class T> class auto_array { private: T* array; mutable bool isReleased; public: explicit auto_array(T* array_ = NULL) : array(array_), isReleased(false) { } auto_array( const auto_array<T> &aarray) { array = aarray.array; isReleased = aarray.isReleased; aarray.isReleased = true; } ~auto_array() { if (!isReleased && array != NULL) { delete[] array; } } T* get() const { return array; } T & operator*() const { return *array; } void operator=(const auto_array<T> &aarray) { if (!isReleased && array != NULL) { delete[] array; } array = aarray.array; isReleased = aarray.isReleased; aarray.isReleased = true; } T* operator->() const { return array; } T* release() { isReleased = true; return array; } void reset(T* array_ = NULL) { if (!isReleased && array != NULL) { delete[] array; } array = array_; } T* operator+(int i) { return array + i; } T & operator[](int i) { return array[i]; } }; } Image* loadBMP( const char* filename) { ifstream input; input.open(filename, ifstream::binary); assert(!input.fail() || ! "Could not find file"); char buffer[2]; input.read(buffer, 2); assert(buffer[0] == 'B' && buffer[1] == 'M' || !"Not a bitmap file"); input.ignore(8); int dataOffset = readInt(input); //Read the header int headerSize = readInt(input); int width; int height; switch(headerSize) { case 40: //V3 width = readInt(input); height = readInt(input); input.ignore(2); assert(readShort(input) == 24 || ! "Image is not 24 bits per pixel"); assert(readShort(input) == 0 || ! "Image is compressed"); break; case 12: //OS/2 V1 width = readShort(input); height = readShort(input); input.ignore(2); assert(readShort(input) == 24 || ! "Image is not 24 bits per pixel"); break; case 64: //OS/2 V2 assert(! "Can't load OS/2 V2 bitmaps"); break; case 108: //Windows V4 assert(! "Can't load Windows V4 bitmaps"); break; case 124: //Windows V5 assert(! "Can't load Windows V5 bitmaps"); break; default: assert(! "Unknown bitmap format"); } //Read the data int bytesPerRow = ((width * 3 + 3) / 4) * 4 - (width * 3 % 4); int size = bytesPerRow * height; auto_array< char> pixels(new char[size]); input.seekg(dataOffset, ios_base::beg); input.read(pixels.get(), size); //Get the data into the right format auto_array< char> pixels2(new char[width * height * 3]); for(int y = 0; y < height; y++) { for(int x = 0; x < width; x++) { for(int c = 0; c < 3; c++) { pixels2[3 * (width * y + x) + c] = pixels[bytesPerRow * y + 3 * x + (2 - c)]; } } } input.close(); return new Image(pixels2.release(), width, height); } ? ? ? ? ? ? ? ? ? //imageloader.h #ifndef IMAGE_LOADER_H_INCLUDED #define IMAGE_LOADER_H_INCLUDED //Represents an image class Image { public: Image( char* ps, int w, int h); ~Image(); /* An array of the form (R1, G1, B1, R2, G2, B2, ...) indicating the * color of each pixel in image. Color components range from 0 to 255. * The array starts the bottom-left pixel, then moves right to the end * of the row, then moves up to the next column, and so on. This is the * format in which OpenGL likes images. */ char* pixels; int width; int height; }; //Reads a bitmap image from file. Image* loadBMP( const char* filename); #endif I get the error: "Can't load windows V4 bitmaps" when i load this image: But it works PERFECTLY when i load this image-> Why can't i load the 1st image? Both images are 256x256, 24bit and BMP files.

Graphics and GPU Programming Programming OpenGL

Started by Shawn619 December 30, 2012 08:09 PM

12 comments, last by deftware 11 years, 3 months ago

GeneralQuery

1,264

December 31, 2012 10:41 PM

All i need is to know how to get the images in the .BMP loader's specification.

Im sorry, but i can't follow your linked tutorial because it is 11 years old and deprecated.

The steps are still valid in MSVS.

deftware

1,778

January 01, 2013 12:26 AM

I made two bitmaps in gimp, one with colorspace information, one without, opened them up in a hex editor, found the byte your code does the switch/case statement on, with colorspace info included the value is 108, without it the value is 40, which is what your code relies on in order to operate. Therefore, either your GIMP version is broken (ignoring the checkbox?) or you're missing something..

On a personal note, this is why I study all file formats and write my own loading code from scratch. I avoid jpeg format because there are seemingly endless variants. Your code looks like it should work just fine with the bitmaps output by GIMP.

If you're getting the SAME windows v4 error, then you are obviously not replacing the actual bitmap file that your program is trying to load.

Shawn619

342

Author

January 01, 2013 04:14 AM

I made two bitmaps in gimp, one with colorspace information, one without, opened them up in a hex editor, found the byte your code does the switch/case statement on, with colorspace info included the value is 108, without it the value is 40, which is what your code relies on in order to operate. Therefore, either your GIMP version is broken (ignoring the checkbox?) or you're missing something..

On a personal note, this is why I study all file formats and write my own loading code from scratch. I avoid jpeg format because there are seemingly endless variants. Your code looks like it should work just fine with the bitmaps output by GIMP.

If you're getting the SAME windows v4 error, then you are obviously not replacing the actual bitmap file that your program is trying to load.

Hey Radio, you're completely right and i appreciate you going the extra step for me. It loads perfectly now. Apparently exporting over the same file does not write over it. What i should have done was use GIMP's "overwrite" function, which didn't exist years ago when i used GIMP. Thanks Radio :)

deftware

1,778

January 03, 2013 05:50 AM

you are welcome, glad I could help ;D

BMP file problem

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BMP file problem

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