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Generating an image?

Started by menorian Apr 12, 2009 at 6:36 PM 4 replies 1k views

Original Post

Apr 12, 2009 at 6:36 PM

hello, i need some help to understand how i can convert my generated image into an unsigned char array that i need for "gluBuild2DMipmaps()" function. the code i wrote to generate the image: short iSize = 128; int x, y; unsigned char data[128][128][4]; for ( x = 0; x < iSize; x++ ) { for ( y = 0; y < iSize; y++ ) { int c = ((((x&0x20)==0)^((y&0x20))==0)); c = c ? 255 : 128; data[x][y][0] = c; data[x][y][1] = c; data[x][y][2] = c; data[x][y][3] = 255; } } unsigned char *imageDATA; // this will eventually become the image data. could anyone help me with this, i dont know how the pixel offset for image data works. Thanks, [Edited by - menorian on April 12, 2009 6:53:03 PM]

Erik Rufelt

189

Erik Rufelt

Apr 12, 2009 at 7:25 PM

Simply use 'data'.. you don't need to do anything with it. Then use gluBuild2DMipmaps(GL_TEXTURE_2D, 4, 128, 128, GL_RGBA, GL_UNSIGNED_BYTE, data). I tried it with your code, and it works fine.

V-man

163

V-man

Apr 12, 2009 at 9:13 PM

I guess your question is, how to make a texture.
http://www.opengl.org/wiki/Texture_Mapping
http://www.opengl.org/wiki/Common_Mistakes#gluBuild2DMipmaps

menorian

Author

menorian

Apr 13, 2009 at 5:23 AM

well it doesn't work.
i do an unsigned char cast (just using data didn't work)
like this:

Texture[0]->imageData = (unsigned char*)data;

but the end result looks like this, and i don't understand why:

i have no idea why those first pixels are broken, any ideas?

Erik Rufelt

189

Erik Rufelt

Apr 13, 2009 at 6:55 AM

Show your entire code, for the part that creates the image and sends it to OpenGL, including any texture parameter settings and the texture creation.

Simulacrum

Apr 13, 2009 at 8:33 AM

You may want to try filling your image data scanline by scanline. Something like this:

const int width(128);const int height (128);     //height equal the number of scanlines in the imageconst int bytesPerPixel(4);const int scanlineSize(width * bytesPerPixel);const unsigned char *imageData(new char[scanlineSize * height]);int offset(0);for(int i(0);i < height;++i){     //pick the value you wish to initialize with     c = (c) ? 255 : 128;     //fill the scanline with the value you want     std::memset(          &imageData[0] + offset,          c,          scanlineSize);      // ^^^ or have another loop here to set each       // pixel value in the scanline...      //for(j(offset);j < (offset + scalineSize);++j){ imageData[j] = "whatever"; }     //housekeeping - update your offset into your image data     offset += scanlineSize;}//housekeeping - delete the dynamic array - Opengl now owns your texture//so you don't need it any longerdelete [] imageData;

I don't know what you expect your texture to look like but perhaps this helps you understand how to use "pixel offsets into image data"?

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