gnome-shell/src/st/st-scroll-view-fade.glsl

/*
 * st-scroll-view-fade.glsl: Edge fade effect for StScrollView
 *
 * Copyright 2010 Intel Corporation.
 * Copyright 2011 Adel Gadllah
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU Lesser General Public License,
 * version 2.1, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
 * more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

uniform sampler2D tex;
uniform float height;
uniform float width;
uniform float vfade_offset;
uniform float hfade_offset;
uniform bool  fade_edges_top;
uniform bool  fade_edges_right;
uniform bool  fade_edges_bottom;
uniform bool  fade_edges_left;

uniform vec2 fade_area_topleft;
uniform vec2 fade_area_bottomright;

void main ()
{
    cogl_color_out = cogl_color_in * texture2D (tex, vec2 (cogl_tex_coord_in[0].xy));

    float y = height * cogl_tex_coord_in[0].y;
    float x = width * cogl_tex_coord_in[0].x;

    /*
     * We cannot just return here due to a bug in llvmpipe see:
     * https://bugzilla.freedesktop.org/show_bug.cgi?id=62357
     */
    if (x > fade_area_topleft[0] && x < fade_area_bottomright[0] &&
        y > fade_area_topleft[1] && y < fade_area_bottomright[1]) {
        float ratio = 1.0;
        float fade_bottom_start = fade_area_bottomright[1] - vfade_offset;
        float fade_right_start = fade_area_bottomright[0] - hfade_offset;
        bool fade_top = y < vfade_offset && fade_edges_top;
        bool fade_bottom = y > fade_bottom_start && fade_edges_bottom;
        bool fade_left = x < hfade_offset && fade_edges_left;
        bool fade_right = x > fade_right_start && fade_edges_right;

        float vfade_scale = height / vfade_offset;
        if (fade_top) {
            ratio *= y / vfade_offset;
        }

        if (fade_bottom) {
            ratio *= (fade_area_bottomright[1] - y) / (fade_area_bottomright[1] - fade_bottom_start);
        }

        float hfade_scale = width / hfade_offset;
        if (fade_left) {
            ratio *= x / hfade_offset;
        }

        if (fade_right) {
            ratio *= (fade_area_bottomright[0] - x) / (fade_area_bottomright[0] - fade_right_start);
        }

        cogl_color_out *= ratio;
    }
}