What would be the appropriate blend function?
Before you upload the texture, loop over the pixels and make the FF00FF pixels transparent (0 alpha).
Then use glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA )
Then use glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA )
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How would I set the alpha using this function to load bitmaps? :
Thank you,
~Axesor
void BmpImg::RESLoadImg(unsigned int idnumber, int num){ HBITMAP hBMP; BITMAP BMP; glGenTextures(1, &g_bmp[num]); hBMP=(HBITMAP)LoadImage(GetModuleHandle(NULL),MAKEINTRESOURCE(idnumber), IMAGE_BITMAP, 0, 0, LR_CREATEDIBSECTION); if (hBMP) { GetObject(hBMP,sizeof(BMP), &BMP); // Buffer For Object Information glPixelStorei(GL_UNPACK_ALIGNMENT,4); // Pixel Storage Mode (Word Alignment / 4 Bytes) glBindTexture(GL_TEXTURE_2D, g_bmp[num]); // Bind Our Texture glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER, GL_NEAREST); // Generate Mipmapped Texture (3 Bytes, Width, Height And Data From The BMP) gluBuild2DMipmaps(GL_TEXTURE_2D, 3, BMP.bmWidth, BMP.bmHeight, GL_BGR_EXT, GL_UNSIGNED_BYTE, BMP.bmBits); DeleteObject(hBMP); // Delete The Bitmap Object }}Thank you,
~Axesor
If bmBitsPixel is three, as it looks like it is, then you would have to allocate a new block of memory with space for the alpha value.
I suggest using TGA and just making the color transparent using your image editor of choice.
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I suggest using TGA and just making the color transparent using your image editor of choice.
Link
Likely another function is needed to convert the HBITMAP to a 32bit alpha bitmap. Since .BMP files cannot have alpha-channels you need to create a shadow bitmap that does. You may need to swap RGBA<->ARGB depending on what you want.
Here is some code and psuedo-code
[Edited by - Jack Sotac on March 28, 2006 7:34:14 PM]
Here is some code and psuedo-code
unsigned char* Bmp24ToBmp32(BITMAP& BMP){//1)Allocate an RGBA bitmapunsigned char* alphabitmap = new char[BMP.bmWidth * BMP.bmHeight * 4]; if(NULL == alphabitmap)return NULL;//2)Calculate pitch (bytes per line)int alphapitch = BMP.bmWidth * 4;//3)Loop though all pixels of the original bitmap for (i = 0;i < BMP.bmHeight;i++) for (j = 0;j < BMP.bmWidth;j++) {//4)Calculate proper byte offset into the bitmaps int offRGBA = i *(alphapitch) + (j*4); int offRGB = i * (BMP.bmWidthBytes) + (j*3);//4a) Get color at (i,j) from source bitmap unsigned int pix = BMP.bmBits[offRGB]&0xFF;//B pix |= BMP.bmBits[offRGB+1]<<8;//G pix |= BMP.bmBits[offRGB+2]<<16;//R//4b) Get pointer to corresponding position in destination bitmap unsigned int* curRGBA = static_cast<unsigned int *>(&alphabitmap[offRGBA]);//4c) Copy source pixel to dest *curRGBA = pix;//5) Check if source color is magenta if(pix == 0x00FF00FF) curRGBA[3] = 0; //6) Set alpha to zero (this pixel will not be seen) else curRGBA[3] = 255; //7) Set alpha to 255 (this pixel will be seen fully) }return alphabitmap;}void BmpImg::RESLoadImg(unsigned int idnumber, int num){ HBITMAP hBMP; BITMAP BMP; glGenTextures(1, &g_bmp[num]); hBMP=(HBITMAP)LoadImage(GetModuleHandle(NULL),MAKEINTRESOURCE(idnumber), IMAGE_BITMAP, 0, 0, LR_CREATEDIBSECTION); if (hBMP) { GetObject(hBMP,sizeof(BMP), &BMP); unsigned char* ptrAlpha = Bmp24ToBmp32(BMP); if(NULL == ptrAlpha)return; // Buffer For Object Information glPixelStorei(GL_UNPACK_ALIGNMENT,4); // Pixel Storage Mode (Word Alignment / 4 Bytes) glBindTexture(GL_TEXTURE_2D, g_bmp[num]); // Bind Our Texture glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER, GL_NEAREST); // Generate Mipmapped Texture (4 Bytes, Width, Height And Data From The BMP) gluBuild2DMipmaps(GL_TEXTURE_2D, 4, BMP.bmWidth, BMP.bmHeight, GL_BGRA_EXT, GL_UNSIGNED_BYTE, BMP.bmBits); delete[] ptrAlpha; DeleteObject(hBMP); // Delete The Bitmap Object }}[Edited by - Jack Sotac on March 28, 2006 7:34:14 PM]
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Seems correct and mainly the way I am loading my bitmaps from a file.
Can you put that in code form? I don't seem how you transfer the resource bitmap.
Can you put that in code form? I don't seem how you transfer the resource bitmap.
GLuint BitmapToTexture(char* filename, COLORREF key/*= RGB(255, 0, 255)*/, unsigned char alpha/*=255*/, unsigned char key_alpha/*=0*/){ GLuint texture = 0; //the return value long width = 0; long height = 0; unsigned long* data = BitmapToRGBA(filename, &width, &height, key, alpha, key_alpha); //finally generate a texture glGenTextures(1, &texture); glBindTexture(GL_TEXTURE_2D, texture); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA4, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data); glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER, GL_LINEAR); delete data; return texture;}unsigned long int* BitmapToRGBA(char* filename, long int* width, long int* height, COLORREF key/*= RGB(255, 0, 255)*/, unsigned char alpha/*=255*/, unsigned char key_alpha/*=0*/){ BITMAP bmp; //used only to get bmp dimensions HDC hDC = CreateCompatibleDC(NULL); //choose DC like the desktop HBITMAP hBitmap = (HBITMAP)LoadImage(NULL, //load the bitmap filename, IMAGE_BITMAP, 0, 0, LR_CREATEDIBSECTION|LR_DEFAULTSIZE|LR_LOADFROMFILE); if(hBitmap == NULL) //bitmap failed to load { return 0; } //get bitmap dimensions GetObject(hBitmap, sizeof(BITMAP), &bmp); //allocate memory for the bitmap COLORREF *data = new COLORREF[bmp.bmWidth * bmp.bmHeight]; //put it into our device context for GetPixel calls SelectObject(hDC, hBitmap); for(int y = 0; y < bmp.bmHeight; y++) { for(int x = 0; x < bmp.bmWidth; x++) { data[x + (y*bmp.bmHeight)] = GetPixel(hDC, x, y); if(key != data[x + (y*bmp.bmHeight)]) { data[x + (y*bmp.bmHeight)] |= (alpha << 24); } else { data[x + (y*bmp.bmHeight)] |= (key_alpha << 24); } } } //if they care about the dimesions, give them back if(width != NULL) { *width = bmp.bmWidth; } if(height != NULL) { *height = bmp.bmHeight; } return data;}GLubyte *data = NULL;if( BMP.bmBitsPixel == 3 ){ data = AlphaPixelize( BMP.bmBits, BMP.bmWidth, BMP.bmHeight );} else return;gluBuild2DMipmaps(GL_TEXTURE_2D, 4, BMP.bmWidth, BMP.bmHeight, GL_ABGR_EXT, GL_UNSIGNED_BYTE, data);free( data );DeleteObject(hBMP);I just realized that bmWidthBytes is 4, so you can probably loop over the bits without creating a new BITMAP or GLubyte[]
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