make bar charts working

Apparently the bar chart polygon points are clockwise and are therefore
culled. Detect and change the front facing setting that case. Disabling
culling does not work here.

Change-Id: I5b243210d1febcbae2126f099455dd1330a5b7d6

chart2/source/view/main/OpenGLRender.cxx

@@ -241,6 +241,7 @@ int OpenGLRender::InitOpenGL(GLWindow aWindow)
     glEnable(GL_TEXTURE_2D);
     glEnable(GL_CULL_FACE);
     glCullFace(GL_BACK);
+    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
     // Enable depth test
     glEnable(GL_DEPTH_TEST);
     // Accept fragment if it closer to the camera than the former one
@@ -1487,6 +1488,31 @@ int OpenGLRender::SetArea2DShapePoint(float x, float y, int listLength)
     return 0;
 }
 
+namespace {
+
+// only 2D
+bool checkCCW(const Area2DPointList& rPoints)
+{
+    if(rPoints.size() < 3)
+        return true;
+
+    GLfloat sum = 0;
+    for(size_t i = 1; i < rPoints.size()/3; i += 3)
+    {
+        GLfloat x1 = rPoints[(i-1)*3];
+        GLfloat x2 = rPoints[i*3];
+        GLfloat y1 = rPoints[(i-1)*3 + 1];
+        GLfloat y2 = rPoints[i*3 + 1];
+        GLfloat prod = (x2-x1)*(y2+y1);
+
+        sum += prod;
+    }
+
+    return (sum <= 0);
+}
+
+}
+
 int OpenGLRender::RenderArea2DShape()
 {
     CHECK_GL_ERROR();
@@ -1501,6 +1527,9 @@ int OpenGLRender::RenderArea2DShape()
     for (size_t i = 0; i < listNum; ++i)
     {
         Area2DPointList &pointList = m_Area2DShapePointList.front();
+        bool bIsCCW = checkCCW(pointList); // is it counter clockwise (CCW) or clockwise (CW)
+        if(!bIsCCW)
+            glFrontFace(GL_CW);
         //fill vertex buffer
         glBindBuffer(GL_ARRAY_BUFFER, m_VertexBuffer);
         glBufferData(GL_ARRAY_BUFFER, pointList.size() * sizeof(float), &pointList[0], GL_STATIC_DRAW);
@@ -1522,9 +1551,12 @@ int OpenGLRender::RenderArea2DShape()
             0,                  // stride
             (void*)0            // array buffer offset
             );
+        // TODO: moggi: remove deprecated GL_POLYGON
         glDrawArrays(GL_POLYGON, 0, pointList.size() / 3); // 12*3 indices starting at 0 -> 12 triangles
         glDisableVertexAttribArray(m_2DVertexID);
         glUseProgram(0);
+        if(!bIsCCW)
+            glFrontFace(GL_CCW);
         m_Area2DShapePointList.pop_front();
     }
     glEnable(GL_MULTISAMPLE);