Webgl 1 bit per pixel texture

Question

Is there any way to use 1 bit per pixel texture data in WebGL (for example texture 16×16px in 32 bytes of data) or is it necessary to unpack data from 1bpp to 8bpp first?

I have found similar OpenGL related question and answer https://stackoverflow.com/a/15706596/4540236, but it seems to me, that WebGL does not have GL_BITMAP data type constant.

Answer 1

WebGL itself has no one bit per pixel format. You'll have to unpack the data yourself.

You can unpack it to 1 byte per pixel with formats gl.ALPHA or gl.LUMINANCE

you could try creating a fragment shader to unpack, no idea if the precision issues would kill you. Something like

precision mediump float;

varying vec2 v_texcoord;
uniform vec2 u_textureSize;
uniform sampler2D u_texture;

void main() {
  float texelCoord = floor(v_texcoord.x * u_textureSize.x); 
  float bit  = mod(texelCoord, 8.0);
  float byte = texelCoord / 8.0;
  vec2 uv = vec2(byte / u_textureSize.x, v_texcoord.y);
  float eightPixels = texture2D(u_texture, uv).r * 255.0;
  float pixel = mod(floor(eightPixels / pow(2.0, bit)), 2.0);
  gl_FragColor = vec4(pixel, pixel, pixel, 1.0);
}

Hmmm I guess we should test ...

// Using TWGL.js because it's easier and I'm lazy
var gl = twgl.getWebGLContext(document.getElementById("c"));
var programInfo = twgl.createProgramInfo(gl, ["vs", "fs"]);

var arrays = {
  position: [-1, -1, 0, 1, -1, 0, -1, 1, 0, -1, 1, 0, 1, -1, 0, 1, 1, 0],
};
var bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);

function render(time) {
  twgl.resizeCanvasToDisplaySize(gl.canvas);
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  var uniforms = {
    u_texture: twgl.createTexture(gl, {
      format: gl.LUMINANCE,
      min: gl.NEAREST,
      mag: gl.NEAREST,
      width: 1,
      src: [ 0x3C, 0x42, 0xBD, 0x81, 0xA5, 0x81, 0x42, 0x3C, ],
    }),
    u_textureSize: [8, 8],
  };

  gl.useProgram(programInfo.program);
  twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);
  twgl.setUniforms(programInfo, uniforms);
  console.log("foo");
  twgl.drawBufferInfo(gl, gl.TRIANGLES, bufferInfo);
}
render();

canvas { border: 1px solid red; }

<script src="//twgljs.org/dist/twgl-full.min.js"></script>
<canvas id="c"></canvas>
  <script id="vs" type="notjs">
attribute vec4 position;
varying vec2 v_texcoord;
void main() {
  gl_Position = position;
  v_texcoord = position.xy * 0.5 + 0.5;
}
  </script>
  <script id="fs" type="notjs">
    precision mediump float;

    varying vec2 v_texcoord;
    uniform vec2 u_textureSize;
    uniform sampler2D u_texture;
    
    void main() {
      float texelCoord = floor(v_texcoord.x * u_textureSize.x); 
      float bit  = mod(texelCoord, 8.0);
      float byte = texelCoord / 8.0;
      vec2 uv = vec2(byte / u_textureSize.x, v_texcoord.y);
      float eightPixels = texture2D(u_texture, uv).r * 255.0;
      float pixel = mod(floor(eightPixels / pow(2.0, bit)), 2.0);
      gl_FragColor = vec4(pixel, pixel, pixel, 1.0);
    }
</script>

Answer 2

As gman answered (https://stackoverflow.com/a/30529136/4540236): WebGL does not support one bit per pixel format.

So I used LUMINANCE format and unpack data manually with:

int off = 0;
for (int i=0;i<packedData.length;i++,off+=8) {
  int val = packedData[i];
  for (int j=0;j<8;j++) {
    unpackedData[off+j] = ((val&(1<<j))!=0)?255:0;        
  }
}