OpenGL and monochrome texture

StackOverflow https://stackoverflow.com/questions/327642

  •  11-07-2019
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Question

Is it possible to pump monochrome (graphical data with 1 bit image depth) texture into OpenGL?

I'm currently using this:

glTexImage2D( GL_TEXTURE_2D, 0, 1, game->width, game->height, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, game->culture[game->phase] );

I'm pumping it with square array of 8 bit unsigned integers in GL_LUMINANCE mode (one 8 bit channel represents brightness of all 3 channels and full alpha), but it is IMO vastly ineffective, because the onlu values in the array are 0x00 and 0xFF.

Can I (and how) use simple one-bit per pixel array of booleans instead somehow? The excessive array size slows down any other operations on the array :(

Was it helpful?

Solution

The smallest uncompressed texture-format for luminance images uses 8 bits per pixel.

However, 1 bit per pixel images can be compressed without loss to the S3TC or DXT format. This will still not be 1 bit per pixel but somewhere between 2 and 3 bits.

If you really need 1 bit per pixel you can do so with a little trick. Load 8 1 bit per pixel textures as one 8 bit Alpha-only texture (image 1 gets loaded into bit 1, image 2 into bit 2 and so on). Once you've done that you can "address" each of the sub-textures using the alpha-test feature and a bit of texture environment programming to turn alpha into a color.

This will of only work if you have 8 1 bit per pixel textures and tricky to get right though.

OTHER TIPS

After some research, I was able to render the 1-bit per pixel image as a texture with the following code:

static GLubyte smiley[] = /* 16x16 smiley face */
{
    0x03, 0xc0, /*       ****       */
    0x0f, 0xf0, /*     ********     */
    0x1e, 0x78, /*    ****  ****    */
    0x39, 0x9c, /*   ***  **  ***   */
    0x77, 0xee, /*  *** ****** ***  */
    0x6f, 0xf6, /*  ** ******** **  */
    0xff, 0xff, /* **************** */
    0xff, 0xff, /* **************** */
    0xff, 0xff, /* **************** */
    0xff, 0xff, /* **************** */
    0x73, 0xce, /*  ***  ****  ***  */
    0x73, 0xce, /*  ***  ****  ***  */
    0x3f, 0xfc, /*   ************   */
    0x1f, 0xf8, /*    **********    */
    0x0f, 0xf0, /*     ********     */
    0x03, 0xc0  /*       ****       */
};

float index[] = {0.0, 1.0};

glPixelStorei(GL_UNPACK_ALIGNMENT,1);

glPixelMapfv(GL_PIXEL_MAP_I_TO_R, 2, index);
glPixelMapfv(GL_PIXEL_MAP_I_TO_G, 2, index);
glPixelMapfv(GL_PIXEL_MAP_I_TO_B, 2, index);
glPixelMapfv(GL_PIXEL_MAP_I_TO_A, 2, index);

glTexImage2D(GL_TEXTURE_2D,0,GL_RGBA,16,16,0,GL_COLOR_INDEX,GL_BITMAP,smiley);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

and here is the result:

enter image description here

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