From e636c316a67bbb2888d25de2036d20149c286120 Mon Sep 17 00:00:00 2001
From: Emmanuele Bassi <ebassi@gnome.org>
Date: Tue, 6 Oct 2015 19:55:43 +0100
Subject: [PATCH] gl: Use older GLSL shaders with legacy contexts

If we're using modern GLSL, then we should stop using deprecated
modifiers, like 'varying' and 'attribute', as well as deprecated global
variables, like 'gl_FragColor'.

On the other hand, with legacy contexts we should be using older GLSL
shaders, to maximize compatibility.

https://bugzilla.gnome.org/show_bug.cgi?id=756142
---
 gdk/gdkgl.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 55 insertions(+), 6 deletions(-)

diff --git a/gdk/gdkgl.c b/gdk/gdkgl.c
index 85ce63da55..81eb40dc66 100644
--- a/gdk/gdkgl.c
+++ b/gdk/gdkgl.c
@@ -147,9 +147,27 @@ bind_vao (GdkGLContextPaintData *paint_data)
 static void
 use_texture_2d_program (GdkGLContextPaintData *paint_data)
 {
-  static const char *vertex_shader_code =
+  static const char *vertex_shader_code_150 =
     "#version 150\n"
     "uniform sampler2D map;"
+    "in vec2 position;\n"
+    "in vec2 uv;\n"
+    "out vec2 vUv;\n"
+    "void main() {\n"
+    "  gl_Position = vec4(position, 0, 1);\n"
+    "  vUv = uv;\n"
+    "}\n";
+  static const char *fragment_shader_code_150 =
+    "#version 150\n"
+    "in vec2 vUv;\n"
+    "out vec4 vertexColor;\n"
+    "uniform sampler2D map;\n"
+    "void main() {\n"
+    "  vertexColor = texture2D (map, vUv);\n"
+    "}\n";
+  static const char *vertex_shader_code_130 =
+    "#version 130\n"
+    "uniform sampler2D map;"
     "attribute vec2 position;\n"
     "attribute vec2 uv;\n"
     "varying vec2 vUv;\n"
@@ -157,14 +175,21 @@ use_texture_2d_program (GdkGLContextPaintData *paint_data)
     "  gl_Position = vec4(position, 0, 1);\n"
     "  vUv = uv;\n"
     "}\n";
-  static const char *fragment_shader_code =
-    "#version 150\n"
+  static const char *fragment_shader_code_130 =
+    "#version 130\n"
     "varying vec2 vUv;\n"
     "uniform sampler2D map;\n"
     "void main() {\n"
     "  gl_FragColor = texture2D (map, vUv);\n"
     "}\n";
 
+  const char *vertex_shader_code = paint_data->is_legacy
+                                 ? vertex_shader_code_130
+                                 : vertex_shader_code_150;
+  const char *fragment_shader_code = paint_data->is_legacy
+                                   ? fragment_shader_code_130
+                                   : fragment_shader_code_150;
+
   if (paint_data->texture_2d_quad_program.program == 0)
     make_program (&paint_data->texture_2d_quad_program, vertex_shader_code, fragment_shader_code);
 
@@ -178,9 +203,9 @@ use_texture_2d_program (GdkGLContextPaintData *paint_data)
 static void
 use_texture_rect_program (GdkGLContextPaintData *paint_data)
 {
-  static const char *vertex_shader_code =
+  static const char *vertex_shader_code_150 =
     "#version 150\n"
-    "uniform sampler2DRect map;"
+    "uniform sampler2DRect map;\n"
     "attribute vec2 position;\n"
     "attribute vec2 uv;\n"
     "varying vec2 vUv;\n"
@@ -188,13 +213,37 @@ use_texture_rect_program (GdkGLContextPaintData *paint_data)
     "  gl_Position = vec4(position, 0, 1);\n"
     "  vUv = uv;\n"
     "}\n";
-  static const char *fragment_shader_code =
+  static const char *fragment_shader_code_150 =
     "#version 150\n"
     "varying vec2 vUv;\n"
     "uniform sampler2DRect map;\n"
     "void main() {\n"
     "  gl_FragColor = texture2DRect (map, vUv);\n"
     "}\n";
+  static const char *vertex_shader_code_130 =
+    "#version 130\n"
+    "uniform sampler2DRect map;\n"
+    "attribute vec2 position;\n"
+    "attribute vec2 uv;\n"
+    "varying vec2 vUv;\n"
+    "void main() {\n"
+    "  gl_Position = vec4(position, 0, 1);\n"
+    "  vUv = uv;\n"
+    "}\n";
+  static const char *fragment_shader_code_130 =
+    "#version 130\n"
+    "varying vec2 vUv;\n"
+    "uniform sampler2DRect map;\n"
+    "void main() {\n"
+    "  gl_FragColor = texture2DRect (map, vUv);\n"
+    "}\n";
+
+  const char *vertex_shader_code = paint_data->is_legacy
+                                 ? vertex_shader_code_130
+                                 : vertex_shader_code_150;
+  const char *fragment_shader_code = paint_data->is_legacy
+                                   ? fragment_shader_code_130
+                                   : fragment_shader_code_150;
 
   if (paint_data->texture_rect_quad_program.program == 0)
     make_program (&paint_data->texture_rect_quad_program, vertex_shader_code, fragment_shader_code);