OpenGL: prepare GLSL for version 3.3

- use in/out instead of attribute/varying
- use named output instead of gl_FragColor
- use texture() instead of the multitude of older texture sampling functions

The #if __VERSION__ == 120 paths (needed on Mac) will be removed after we switch to 3.3 core profile.

Part of T49165 (general OpenGL upgrade)

source/blender/gpu/intern/gpu_codegen.c

@@ -653,7 +653,7 @@ static void codegen_call_functions(DynStr *ds, ListBase *nodes, GPUOutput *final
 		BLI_dynstr_append(ds, ");\n");
 	}
 
-	BLI_dynstr_append(ds, "\n\tgl_FragColor = ");
+	BLI_dynstr_append(ds, "\n\tfragColor = ");
 	codegen_convert_datatype(ds, finaloutput->type, GPU_VEC4, "tmp", finaloutput->id);
 	BLI_dynstr_append(ds, ";\n");
 }

source/blender/gpu/shaders/gpu_shader_fire_frag.glsl

@@ -1,5 +1,13 @@
 
-varying vec3 coords;
+#if __VERSION__ == 120
+  varying vec3 coords;
+  #define fragColor gl_FragColor
+#else
+  in vec3 coords;
+  out vec4 fragColor;
+  #define texture1D texture
+  #define texture3D texture
+#endif
 
 uniform sampler3D flame_texture;
 uniform sampler1D spectrum_texture;
@@ -13,5 +21,5 @@ void main()
 	color.rgb = emission.a * emission.rgb;
 	color.a = emission.a;
 
-	gl_FragColor = color;
+	fragColor = color;
 }

source/blender/gpu/shaders/gpu_shader_material.glsl

@@ -5,6 +5,14 @@ uniform mat4 ModelViewMatrixInverse;
 uniform mat4 ProjectionMatrixInverse;
 uniform mat3 NormalMatrix;
 
+#if __VERSION__ == 120
+  #define fragColor gl_FragColor
+#else
+  out vec4 fragColor;
+  #define texture2D texture
+  #define textureCube texture
+#endif
+
 /* Converters */
 
 float convert_rgba_to_float(vec4 color)

source/blender/gpu/shaders/gpu_shader_smoke_frag.glsl

@@ -1,5 +1,13 @@
 
-varying vec3 coords;
+#if __VERSION__ == 120
+  varying vec3 coords;
+  #define fragColor gl_FragColor
+#else
+  in vec3 coords;
+  out vec4 fragColor;
+  #define texture1D texture
+  #define texture3D texture
+#endif
 
 uniform vec3 active_color;
 uniform float step_size;
@@ -44,5 +52,5 @@ void main()
 	vec4 color = transfer_function * density_scale;
 #endif
 
-	gl_FragColor = color;
+	fragColor = color;
 }

source/blender/gpu/shaders/gpu_shader_smoke_vert.glsl

@@ -1,7 +1,11 @@
 
 uniform mat4 ModelViewProjectionMatrix;
 
-varying vec3 coords;
+#if __VERSION__ == 120
+  varying vec3 coords;
+#else
+  out vec3 coords;
+#endif
 
 uniform vec3 min_location;
 uniform vec3 invsize;

source/blender/gpu/shaders/gpu_shader_vertex.glsl

@@ -12,8 +12,13 @@ out block {
 } outpt;
 #endif
 
-varying vec3 varposition;
-varying vec3 varnormal;
+#if __VERSION__ == 120
+  varying vec3 varposition;
+  varying vec3 varnormal;
+#else
+  out vec3 varposition;
+  out vec3 varnormal;
+#endif
 
 #ifdef CLIP_WORKAROUND
 varying float gl_ClipDistance[6];

source/blender/gpu/shaders/gpu_shader_vertex_world.glsl

@@ -1,7 +1,11 @@
 
-varying vec3 varposition;
-varying vec3 varnormal;
-
+#if __VERSION__ == 120
+  varying vec3 varposition;
+  varying vec3 varnormal;
+#else
+  out vec3 varposition;
+  out vec3 varnormal;
+#endif
 
 /* Color, keep in sync with: gpu_shader_vertex.glsl */
 

source/blender/gpu/shaders/gpu_shader_vsm_store_frag.glsl

@@ -2,7 +2,13 @@
  * This fragment shader was initially found at http://fabiensanglard.net/shadowmappingVSM/index.php
  */
 
-varying vec4 v_position;
+#if __VERSION__ == 120
+  varying vec4 v_position;
+  #define fragColor gl_FragColor
+#else
+  in vec4 v_position;
+  out vec4 fragColor;
+#endif
 
 void main()
 {
@@ -17,5 +23,6 @@ void main()
 	float dy = dFdy(depth);
 	moment2 += 0.25 * (dx * dx + dy * dy);
 
-	gl_FragColor = vec4(moment1, moment2, 0.0, 0.0);
+	fragColor = vec4(moment1, moment2, 0.0, 0.0);
+	// TODO: write to a 2-component target --^
 }

source/blender/gpu/shaders/gpu_shader_vsm_store_vert.glsl

@@ -1,6 +1,11 @@
 
 uniform mat4 ModelViewProjectionMatrix;
-varying vec4 v_position;
+
+#if __VERSION__ == 120
+  varying vec4 v_position;
+#else
+  out vec4 v_position;
+#endif
 
 void main()
 {