Create a texture from a [OpenGL-type] bitmap

spiffgq · 2003-03-06T16:19:44

I''m trying to create a texture object in OpenGL from a bitmap. (And by bitmap, I mean a true one-bit-per-pixel OpenGL type bitmap, not that Microsoft abomination file type.) My first thought was to just use glTexImage2D as follows: const unsigned char BITMAP_DATA [] = { /* pixels are here */ }; const int BITMAP_PITCH = 1; // Number of bytes per row const int BITMAP_ROWS = 12; // Number of rows (the height) const int BITMAP_COLS = 8; // Number of pixels per column // Some code goes here blah blah blah unsigned int texObj; glGenTextures (1, &texObj); glBindTexture (GL_TEXTURE_2D, texObj); glTexImage2D ( GL_TEXTURE_2D, 0, GL_INTENSITY, BITMAP_COLS, BITMAP_ROWS, 0, GL_LUMINANCE, GL_BITMAP, BITMAP_DATA ); // and so on Unfortunately, this doesn''t work. The resulting "texture" is just a solid color and does not contain the bitmap''s pixels. glBindTexture (GL_TEXTURE_2D, texObj); glBegin (GL_QUADS); glColor3f (1.0, 0.0, 0.0); glTexCoord2f (0.0, 1.0); glVertex3f ( 0.0f, 0.0f, 0.0f); glTexCoord2f (1.0, 1.0); glVertex3f (300.0f, 0.0f, 0.0f); glTexCoord2f (1.0, 0.0); glVertex3f (300.0f, 300.0f, 0.0f); glTexCoord2f (0.0, 0.0); glVertex3f ( 0.0f, 300.0f, 0.0f); glEnd (); The above code creates a solid red rectangle instead of showing the pixels of the bitmap. Am I on the right track or do I need to go another route completely? If I am on the right track, what am I doing wrong? Thanks for your help.

Graphics and GPU Programming Programming OpenGL

Started by spiffgq March 04, 2003 07:42 PM

9 comments, last by spiffgq 21 years, 1 month ago

Brother Bob

10,350

March 06, 2003 04:19 PM

quote:
const int BITMAP_ROWS = 12;
const int BITMAP_COLS = 8 * BITMAP_PITCH;

If these are the width and height of the texture, the width is wrong. Your image is still 8 bits wide, not 8*4. The extra padding has nothing to do with the texture data, but with pointer alignment after each row is read.

And after looking in the spec (you should look there too concerning what parameters to pass), you should pass GL_BITMAP as the second last parameter, and if you do, you must pass GL_COLOR_INDEX as third last parameter. Like this.

glTexImage2D (   ...   GL_COLOR_INDEX,    GL_BITMAP,    BITMAP_DATA);

This is the only valid combination including GL_BITMAP.

After reading through the specification quickly, I get the impression you can''t use bitmaps as "normal" textures. I strongly suggest you have a look in the specification, you find it here.

Create a texture from a [OpenGL-type] bitmap

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