slang-shaders/border/shaders/blur_fill/scaling.slang

// See compose.slang for copyright and other information.

// Pixels in input coord. space
vec2 eff_input_res() {
    if (param.CENTER_CROP > 0.5) {
        return param.InputSize.xy -
               vec2(param.OS_CROP_LEFT + param.OS_CROP_RIGHT,
                    param.OS_CROP_TOP + param.OS_CROP_BOTTOM);
    }
    return param.InputSize.xy -
           2.0 * vec2(min(param.OS_CROP_LEFT, param.OS_CROP_RIGHT),
                      min(param.OS_CROP_TOP, param.OS_CROP_BOTTOM));
}

// Output to input scaling, in unit coordinate systems.
vec2 scale_o2i() {
    const vec2 eff_input_res = eff_input_res();
    const vec2 eff_aspect =
        vec2(eff_input_res.x, param.FORCE_ASPECT_RATIO > 0.5
                                  ? eff_input_res.y / param.InputSize.y *
                                        param.InputSize.x * param.ASPECT_V /
                                        param.ASPECT_H
                                  : eff_input_res.y);
    if (param.FinalViewportSize.x / eff_aspect.x <
        param.FinalViewportSize.y / eff_aspect.y) {
        // Scale will be limited by width. Calc x scale, then derive y scale
        // using aspect ratio.
        const float scale_x =
            param.FORCE_INTEGER_SCALING > 0.5
                ? floor(param.FinalViewportSize.x / eff_input_res.x)
                : param.FinalViewportSize.x / eff_input_res.x;
        const float scale_y = scale_x * eff_input_res.x * eff_aspect.y /
                              (eff_input_res.y * eff_aspect.x);
        return param.FinalViewportSize.xy * param.InputSize.zw /
               vec2(scale_x, scale_y);
    } else {
        // Scale will be limited by height.
        const float scale_y =
            param.FORCE_INTEGER_SCALING > 0.5
                ? floor(param.FinalViewportSize.y / eff_input_res.y)
                : param.FinalViewportSize.y / eff_input_res.y;
        const float scale_x = scale_y * eff_input_res.y * eff_aspect.x /
                              (eff_input_res.x * eff_aspect.y);
        return param.FinalViewportSize.xy * param.InputSize.zw /
               vec2(scale_x, scale_y);
    }
}

// Input to output scaling, in unit coordinate systems.
vec2 scale_i2o() { return 1.0 / scale_o2i(); }

// Get adjusted center in input unit coordinate system.
vec2 get_input_center() {
    return param.CENTER_CROP > 0.5
               ? 0.5 * param.InputSize.zw *
                     vec2(param.OS_CROP_LEFT + param.InputSize.x -
                              param.OS_CROP_RIGHT,
                          param.OS_CROP_TOP + param.InputSize.y -
                              param.OS_CROP_BOTTOM)
               : vec2(0.49999);
}

// In unit space (output to input).
// coord_in_input_space = o2i(coord_in_output_space)
// This is used to sample from the input texture in the output pass.
vec2 o2i(vec2 x) { return (x - 0.49999) * scale_o2i() + get_input_center(); }

// In unit coordinate systems.
vec2 i2o(vec2 x) { return (x - get_input_center()) * scale_i2o() + 0.49999; }