Method bc3

src/renderware/utils/ImageDecoder.ts:258–365

(data: Uint8Array, width: number, height: number, premultiplied: boolean)

        in DXT4, the color data is interpreted as being premultiplied by alpha
    */
    static bc3(data: Uint8Array, width: number, height: number, premultiplied: boolean): Uint8Array {
        const rgba = new Uint8Array(4 * width * height);
        const alphaPalette = new Uint8Array(8);
        const colorPalette = new Uint8Array(16);
        const alphaIndices = new Uint8Array(16);
        let offset = 0;

        for (let y = 0; y < height; y += 4) {
            for (let x = 0; x < width; x += 4) {
                const alpha0 = data[offset++];
                const alpha1 = data[offset++];

                const alphaBits = data.subarray(offset, offset + 6);
                offset += 6;

                const color0 = ImageDecoder.readUInt16LE(data, offset);
                const color1 = ImageDecoder.readUInt16LE(data, offset + 2);
                let colorBits = ImageDecoder.readUInt32LE(data, offset + 4);
                offset += 8;

                let [c0r, c0g, c0b] = ImageDecoder.decode565(color0);
                let [c1r, c1g, c1b] = ImageDecoder.decode565(color1);

                if (color0 > color1) {
                    colorPalette[0] = c0r; colorPalette[1] = c0g; colorPalette[2] = c0b;
                    colorPalette[4] = c1r; colorPalette[5] = c1g; colorPalette[6] = c1b;
                    colorPalette[8] = (2 * c0r + c1r) / 3;
                    colorPalette[9] = (2 * c0g + c1g) / 3;
                    colorPalette[10] = (2 * c0b + c1b) / 3;
                    colorPalette[12] = (c0r + 2 * c1r) / 3;
                    colorPalette[13] = (c0g + 2 * c1g) / 3;
                    colorPalette[14] = (c0b + 2 * c1b) / 3;
                }
                else {
                    colorPalette[0] = c0r; colorPalette[1] = c0g; colorPalette[2] = c0b;
                    colorPalette[4] = c1r; colorPalette[5] = c1g; colorPalette[6] = c1b;
                    colorPalette[8] = (c0r + c1r) >> 1;
                    colorPalette[9] = (c0g + c1g) >> 1;
                    colorPalette[10] = (c0b + c1b) >> 1;
                    colorPalette[12] = 0; colorPalette[13] = 0; colorPalette[14] = 0;
                }

                if (alpha0 > alpha1) {
                    alphaPalette[0] = alpha0;
                    alphaPalette[1] = alpha1;
                    alphaPalette[2] = (alpha0 * 6 + alpha1 * 1 + 3) / 7;
                    alphaPalette[3] = (alpha0 * 5 + alpha1 * 2 + 3) / 7;
                    alphaPalette[4] = (alpha0 * 4 + alpha1 * 3 + 3) / 7;
                    alphaPalette[5] = (alpha0 * 3 + alpha1 * 4 + 3) / 7;
                    alphaPalette[6] = (alpha0 * 2 + alpha1 * 5 + 3) / 7;
                    alphaPalette[7] = (alpha0 * 1 + alpha1 * 6 + 3) / 7;
                }
                else {
                    alphaPalette[0] = alpha0;
                    alphaPalette[1] = alpha1;
                    alphaPalette[2] = (alpha0 * 4 + alpha1 * 1 + 2) / 5;
                    alphaPalette[3] = (alpha0 * 3 + alpha1 * 2 + 2) / 5;
                    alphaPalette[4] = (alpha0 * 2 + alpha1 * 3 + 2) / 5;