getValueSaturationTexture

pub fn getValueSaturationTexture(hue: f32) dvui.Backend.TextureError!dvui.Texture {
    var h = dvui.fnv.init();
    h.update("value");
    h.update(std.mem.asBytes(&(hue * 10000)));
    const id = h.final();
    if (dvui.textureGetCached(id)) |cached| return cached else {
        var pixels: [4]Color.PMA = .{ .white, .cast(Color.HSV.toColor(.{ .h = hue })), .black, .black };
        // set top right corner to the max value of that hue
        const texture = try dvui.textureCreate(&pixels, .{ .width = 2, .height = 2 });
        dvui.textureAddToCache(id, texture);
        return texture;
    }
}