opengl: Handle stroked semi-circles

And filled but we don't use those yet.  No pixel-alignment needed for
stroked semi-circles (I think) as we set the pixel width to be 1
regardless of the zoom level.

Fixes: lp:1816263
* https://bugs.launchpad.net/kicad/+bug/1816263

common/gal/opengl/gl_builtin_shaders.cpp

@@ -152,7 +152,6 @@ void computeCircleCoords( float vertexIndex, float radius, float lineWidth )
     vec4 center = roundv( gl_ModelViewProjectionMatrix * gl_Vertex + vec4(1, 1, 0, 0), screenPixelSize );
     float pixelWidth = roundr( lineWidth / worldPixelSize, 1.0);
     float pixelR =  roundr( radius / worldPixelSize, 1.0);
-    //float pixelWidth = lineWidth / worldPixelSize;
 
     vec4 adjust = vec4(-1, -1, 0, 0);
 
@@ -174,7 +173,21 @@ void computeCircleCoords( float vertexIndex, float radius, float lineWidth )
         circleCoords = vec2( 0.0, 2.0 );
         delta = vec4( 0, 2 * pixelR, 0, 0 );
     }
-
+    else if( vertexIndex == 4.0 )
+    {
+        circleCoords = vec2( -sqrt( 3.0 ), 0.0 );
+        delta = vec4( 0, 0, 0, 0 );
+    }
+    else if( vertexIndex == 5.0 )
+    {
+        circleCoords = vec2( sqrt( 3.0 ), 0.0 );
+        delta = vec4( 0, 0, 0, 0 );
+    }
+    else if( vertexIndex == 6.0 )
+    {
+        circleCoords = vec2( 0.0, 2.0 );
+        delta = vec4( 0, 0, 0, 0 );
+    }
 
     shaderParams[2] = pixelR;
     shaderParams[3] = pixelWidth;

common/gal/opengl/opengl_gal.cpp

@@ -617,6 +617,7 @@ void OPENGL_GAL::DrawSegment( const VECTOR2D& aStartPoint, const VECTOR2D& aEndP
         // Outlined tracks
         double lineLength = startEndVector.EuclideanNorm();
 
+        SetLineWidth( 1.0 );
         currentManager->Color( strokeColor.r, strokeColor.g, strokeColor.b, strokeColor.a );
 
         Save();