Add Sixel support

Fixes #910

1 files changed, 40 insertions, 0 deletions

diff --git a/alacritty/res/graphics.f.glsl b/alacritty/res/graphics.f.glsl
new file mode 100644
index 00000000..28da2a68
--- /dev/null
+++ b/alacritty/res/graphics.f.glsl
@@ -0,0 +1,40 @@
+#version 330 core
+
+// Index in the textures[] uniform.
+flat in int texId;
+
+// Texture coordinates.
+in vec2 texCoords;
+
+// Array with graphics data.
+uniform sampler2D textures[16];
+
+// Computed color.
+out vec4 color;
+
+void main() {
+    // The expression `textures[texId]` can't be used in OpenGL 3.3.
+    // If we try to use it, the compiler throws this error:
+    //
+    //     sampler arrays indexed with non-constant expressions
+    //     are forbidden in GLSL 1.30 and later
+    //
+    // To overcome this limitation we use a switch for every valid
+    // value of `texId`.
+    //
+    // The first expression (`textures[texId]`) works with OpenGL 4.0
+    // or later (using `#version 400 core`). If Alacritty drops support
+    // for OpenGL 3.3, this switch block can be replaced with it.
+
+
+#define TEX(N) case N: color = texture(textures[N], texCoords); break;
+
+    switch(texId) {
+        TEX( 0) TEX( 1) TEX( 2) TEX( 3)
+        TEX( 4) TEX( 5) TEX( 6) TEX( 7)
+        TEX( 8) TEX( 9) TEX(10) TEX(11)
+        TEX(12) TEX(13) TEX(14) TEX(15)
+        default:
+            discard;
+    }
+}