improve GLSL classification (#4692)

* added extensions .gs, .comp and .glslf.
  See: https://stackoverflow.com/q/6432838

* add disambiguation rule for .gs files:
  if it starts with `#version <number>`, it's GLSL.
  This seems to work for most GLSL files with few exceptions
  that are catched by the classifier.

* added sample extrude_normal.gs from kyle-piddington/ShaderTool
  (licensed under MIT):
  https://github.com/kyle-piddington/ShaderTool/blob/c753a53bde6eab942da617adab9483c945f27f51/assets/shaders/extrude_normals.gs

* added sample blend_120.glslf from gfx-rs/gfx (licensed under
  Apache 2.0):
  https://github.com/gfx-rs/gfx/blob/7b084cfbb95e3e4d1ea51e91746fc75b2efb3be3/examples/blend/shader/blend_120.glslf

* test_heuristics.rb now supports alt_name to ake a different file name
for a fixture.

lib/linguist/heuristics.yml

@@ -183,6 +183,8 @@ disambiguations:
   - language: Game Maker Language
 - extensions: ['.gs']
   rules:
+  - language: GLSL
+    pattern: '^#version\s+[0-9]+\b'
   - language: Gosu
     pattern: '^uses java\.'
 - extensions: ['.h']

lib/linguist/languages.yml

@@ -1614,7 +1614,9 @@ GLSL:
   - ".fshader"
   - ".geo"
   - ".geom"
+  - ".glslf"
   - ".glslv"
+  - ".gs"
   - ".gshader"
   - ".shader"
   - ".tesc"

samples/GLSL/blend_120.glslf

@@ -0,0 +1,53 @@
+#version 120
+
+#define SCREEN 0
+#define DODGE 1
+#define BURN 2
+#define OVERLAY 3
+#define MULTIPLY 4
+#define ADD 5
+#define DIVIDE 6
+#define GRAIN_EXTRACT 7
+#define GRAIN_MERGE 8
+
+// grayscale
+uniform sampler2D t_Lena;
+// rgba
+uniform sampler2D t_Tint;
+
+uniform int i_Blend;
+
+varying vec2 v_Uv;
+
+void main() {
+    // we sample from both textures using the same uv coordinates. since our
+    // lena image is grayscale, we only get the first component.
+    vec3 lena = vec3(texture2D(t_Lena, v_Uv).r);
+    vec3 tint = texture2D(t_Tint, v_Uv).rgb;
+
+    vec3 result = vec3(0.0);
+
+    // normally you'd have a shader program per technique, but for the sake of
+    // simplicity we'll just branch on it here.
+    if (i_Blend == SCREEN) {
+        result = vec3(1.0) - ((vec3(1.0) - lena) * (vec3(1.0) - tint));
+    } else if (i_Blend == DODGE) {
+        result = lena / (vec3(1.0) - tint);
+    } else if (i_Blend == BURN) {
+        result = vec3(1.0) - ((vec3(1.0) - lena) / lena);
+    } else if (i_Blend == OVERLAY) {
+        result = lena * (lena + (tint * 2) * (vec3(1.0) - lena));
+    } else if (i_Blend == MULTIPLY) {
+        result = lena * tint;
+    } else if (i_Blend == ADD) {
+        result = lena + tint;
+    } else if (i_Blend == DIVIDE) {
+        result = lena / tint;
+    } else if (i_Blend == GRAIN_EXTRACT) {
+        result = lena - tint + 0.5;
+    } else if (i_Blend == GRAIN_MERGE) {
+        result = lena + tint - 0.5;
+    }
+
+    gl_FragColor = vec4(result, 1.0);
+}

samples/GLSL/extrude_normals.gs

@@ -0,0 +1,27 @@
+#version 330 core
+layout(triangles) in;
+layout (line_strip, max_vertices = 6) out;
+
+in VS_OUT
+{
+   vec3 normal;
+}gs_in[];
+
+const float MAGNITUDE = 0.025f;
+
+void GenerateLine(int index)
+{
+    gl_Position = gl_in[index].gl_Position;
+    EmitVertex();
+    gl_Position = gl_in[index].gl_Position + vec4(gs_in[index].normal, 0.0f) * MAGNITUDE;
+    EmitVertex();
+    EndPrimitive();
+}
+
+void main()
+{
+   GenerateLine(0);
+   GenerateLine(1);
+   GenerateLine(2);
+}
+

test/test_heuristics.rb

@@ -203,10 +203,15 @@ def test_gml_by_heuristics
       })
   end
 
+  # Candidate languages = ["Genie", "GLSL", "Gosu", "JavaScript"]
   def test_gs_by_heuristics
     assert_heuristics({
-      "Gosu" => all_fixtures("Gosu", "*.gs")
+      "GLSL" => all_fixtures("GLSL", "*.gs"),
+      "Gosu" => all_fixtures("Gosu", "*.gs"),
     })
+    assert_heuristics({
+      nil => all_fixtures("Genie", "*.gs") + all_fixtures("JavaScript")
+    }, alt_name="test.gs")
   end
 
   # Candidate languages = ["C++", "Objective-C"]