Implement BLIND_LR effect

Very frequently used across many games.

shaders/effects/blind_lr.f.glsl

@@ -0,0 +1,42 @@
+/* Copyright (C) 2019 Nunuhara Cabbage <nunuhara@haniwa.technology>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://gnu.org/licenses/>.
+ */
+
+uniform sampler2D tex;   // the new scene
+uniform sampler2D old;   // the old scene
+uniform vec2 resolution; // the screen resolution
+uniform float progress;  // effect progress (0..1)
+
+in vec2 tex_coord;
+out vec4 frag_color;
+
+#define NR_BANDS 14
+#define BAND_WIDTH 15
+#define EFFECT_WIDTH (NR_BANDS * BAND_WIDTH)
+
+void main() {
+        // start position of effect
+        float lhs = ((resolution.x + EFFECT_WIDTH) * progress) - EFFECT_WIDTH;
+        // current pixel x-coordinate
+        float p = tex_coord.x * resolution.x;
+        // band index
+        float band_no = (p - lhs) / 15.0;
+        // offset into the band
+        float offset = mod(p - lhs, 15.0);
+        // if offset >= band_no, use new texture
+        float new = step(band_no, offset);
+        vec3 col = mix(texture(old, tex_coord).rgb, texture(tex, tex_coord).rgb, new);
+        frag_color = vec4(col, 1.0);
+}

src/effect.c

@@ -130,12 +130,14 @@ static void render_effect_shader(struct effect_shader *shader, Texture *old, Tex
 #define EFFECT_SHADER(path) { .s = { .prepare = prepare_effect_shader }, .f_path = path}
 static struct effect_shader crossfade_shader = EFFECT_SHADER("shaders/effects/crossfade.f.glsl");
 static struct effect_shader mosaic_shader = EFFECT_SHADER("shaders/effects/mosaic.f.glsl");
+static struct effect_shader blind_lr_shader = EFFECT_SHADER("shaders/effects/blind_lr.f.glsl");
 
 extern GLuint main_surface_fb;
 
 static struct effect_shader *effect_shaders[NR_EFFECTS] = {
 	[EFFECT_CROSSFADE] = &crossfade_shader,
 	[EFFECT_CROSSFADE_MOSAIC] = &mosaic_shader,
+	[EFFECT_BLIND_LR] = &blind_lr_shader,
 };
 
 int sact_Effect(int type, possibly_unused int time, possibly_unused int key)