Why grayscale image use 4 bytes per pixel in VRAM?

yusjoel · July 31, 2020, 10:49am

I create a 1024x1024 AO Map, i think it use 1k1k1byte(=1M) in VRAM, but it use more then 4MB in VRAM.

Leonidas · July 31, 2020, 11:01am

Hi @yusjoel and welcome,

All images uploaded to the GPU contain all color channels (RGBA), regardless if they are only using a single one.

I think that’s the case of how the GPU/WebGL functions with the supported texture formats.

will · August 1, 2020, 12:17am

That’s not quite true actually. When the engine loads a JPG, you get an R8_G8_B8 texture. Else (almost certainly a PNG although I think GIFs are supported too) you get an R8_G8_B8_A8 texture.

github.com

playcanvas/engine/blob/master/src/resources/parser/texture/img.js#L40


    }
    if (this.useImageBitmap) {
        this._loadImageBitmap(url.load, url.original, crossOrigin, callback);
    } else {
        this._loadImage(url.load, url.original, crossOrigin, callback);
    }
},


open: function (url, data, device) {
    var ext = path.getExtension(url).toLowerCase();
    var format = (ext === ".jpg" || ext === ".jpeg") ? PIXELFORMAT_R8_G8_B8 : PIXELFORMAT_R8_G8_B8_A8;
    var texture = new Texture(device, {
        name: url,
        // #ifdef PROFILER
        profilerHint: TEXHINT_ASSET,
        // #endif
        width: data.width,
        height: data.height,
        format: format
    });
    texture.setSource(data);