Avoid using `tan` as identifier in shaders.

This conflicts with the tan() function, currently only on macOS.

res/shaders/edge.vert

@@ -7,7 +7,7 @@ const float feather = 0.5;
 
 attribute vec3 pos;
 attribute vec3 loc;
-attribute vec3 tan;
+attribute vec3 tgt;
 
 uniform mat4 modelview;
 uniform mat4 projection;
@@ -21,7 +21,7 @@ void main() {
     vec3 dir = vec3(modelview[0].z, modelview[1].z, modelview[2].z);
 
     // calculate line contour extension basis for constant width and caps
-    vec3 norm = normalize(cross(tan, dir));
+    vec3 norm = normalize(cross(tgt, dir));
     norm = normalize(norm - dir * dot(dir, norm));
     vec3 perp = normalize(cross(dir, norm));
 

res/shaders/outline.vert

@@ -11,7 +11,7 @@ const float feather = 0.5;
 
 attribute vec3 pos;
 attribute vec4 loc;
-attribute vec3 tan;
+attribute vec3 tgt;
 attribute vec3 nol;
 attribute vec3 nor;
 
@@ -40,7 +40,7 @@ void main() {
                           (mode == EMPHASIZED_WITHOUT_CONTOUR && isTagged && !isOutline));
 
     // calculate line contour extension basis for constant width and caps
-    vec3 norm = normalize(cross(tan, dir));
+    vec3 norm = normalize(cross(tgt, dir));
     norm = normalize(norm - dir * dot(dir, norm));
     vec3 perp = normalize(cross(dir, norm));
 

src/render/gl3shader.cpp

@@ -453,7 +453,7 @@ void EdgeRenderer::Init(const StippleAtlas *a) {
         {
             { ATTRIB_POS, "pos" },
             { ATTRIB_LOC, "loc" },
-            { ATTRIB_TAN, "tan" }
+            { ATTRIB_TAN, "tgt" }
         }
     );
 }
@@ -638,7 +638,7 @@ void OutlineRenderer::Init(const StippleAtlas *a) {
         {
             { ATTRIB_POS, "pos" },
             { ATTRIB_LOC, "loc" },
-            { ATTRIB_TAN, "tan" },
+            { ATTRIB_TAN, "tgt" },
             { ATTRIB_NOL, "nol" },
             { ATTRIB_NOR, "nor" }
         }