persistent buffers not 32-bit

[dtristram]

when buffers are marked PERSISTENT, they no longer respect the FLOAT designation, that is, they become 8-bit per component buffers even when FLOAT: true is specified.

In this patch normalized fragment coordinates are stored in a buffer. If they are stored at 32-bit floats, there is sufficient precision to use them to index image pixels. But if they are 8-bit, then when used to index an image, the image looks blocky because multiple image coordinates are rounded to particular 8-bit values.

The patch has two buffers, both designated as FLOAT. However, the second one is designated PERSISTENT and is unexpectedly limited to 8-bit. The final pass alternately uses the two buffers to index the input image.

Code: Select all

/*{
    "CREDIT": "dtristram",
    "DESCRIPTION": "demonstrates bug where persistent buffers do not respect FLOAT designation, note that when reading from persistent buffer, texture coordinates do not have sufficient precision to address image resolution",
    "CATEGORIES": [ "generator" ],
    "INPUTS": [
        {
            "TYPE": "image",
            "NAME": "inputImage",
            "LABEL": "Image",
        }
    ],
    "PASSES": [
        {
	    "TARGET": "store1",
	    "FLOAT": true,
	    "PERSISTENT": false,
	},
        {
	    "TARGET": "store2",
	    "FLOAT": true,
	    "PERSISTENT": true,
	},
	{
	}
    ]
}*/

float delay = 1;

void main() {
  vec2 uv = isf_FragNormCoord.xy;
  vec4 c = vec4(0,0,1,1);
  
  switch (PASSINDEX) {

  case 0:
  case 1:
    c = vec4(uv, 0, 1);
    break;

  case 2:
    if (fract(TIME/(2*delay)) < 0.5) {
      uv = IMG_THIS_PIXEL(store1).xy;
    } else {
      uv = IMG_THIS_PIXEL(store2).xy;
    }
    
    c = IMG_NORM_PIXEL(inputImage, uv.xy);
    break;
  }
  
  gl_FragColor = c;
}

[Zoltán]

Thanks for letting us know, made a ticket.