From ad491f201ad35c8ab3a687f40dfc4d0680c61cb7 Mon Sep 17 00:00:00 2001
From: Markus Mohrhard <markus.mohrhard@googlemail.com>
Date: Tue, 4 Feb 2014 22:01:37 +0100
Subject: 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 | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

(limited to 'chart2/source')

diff --git a/chart2/source/view/main/OpenGLRender.cxx b/chart2/source/view/main/OpenGLRender.cxx
index 5e1f5dda1dd0..74eb078f5bfc 100755
--- a/chart2/source/view/main/OpenGLRender.cxx
+++ b/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);
-- 
cgit