tutorial: minor shader tweaks in the line plot shader.

tutorial/04_texture.lolfx

@@ -52,21 +52,19 @@ void main(void)
     vec2 tc0 = tc1 - vec2(1.0, 1.0) / 128.0;
     vec2 tc3 = tc2 + vec2(1.0, 1.0) / 128.0;
 
-    float c0 = texture2D(u_Texture, tc0).x;
-    float c1 = texture2D(u_Texture, tc1).x;
-    float c2 = texture2D(u_Texture, tc2).x;
-    float c3 = texture2D(u_Texture, tc3).x;
+    vec4 c;
+    c[0] = texture2D(u_Texture, tc0).x;
+    c[1] = texture2D(u_Texture, tc1).x;
+    c[2] = texture2D(u_Texture, tc2).x;
+    c[3] = texture2D(u_Texture, tc3).x;
 
     /* Artificially compress in Y */
-    c0 *= 0.3;
-    c1 *= 0.3;
-    c2 *= 0.3;
-    c3 *= 0.3;
-
-    vec2 p0 = vec2(tc0.x * width, c0 * height);
-    vec2 p1 = vec2(tc1.x * width, c1 * height);
-    vec2 p2 = vec2(tc2.x * width, c2 * height);
-    vec2 p3 = vec2(tc3.x * width, c3 * height);
+    c *= 0.3;
+
+    vec2 p0 = vec2(tc0.x * width, c[0] * height);
+    vec2 p1 = vec2(tc1.x * width, c[1] * height);
+    vec2 p2 = vec2(tc2.x * width, c[2] * height);
+    vec2 p3 = vec2(tc3.x * width, c[3] * height);
     vec2 a = vec2(t.x * width, t.y * height);
 
     float d0 = point2segment(p0, p1, a);