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PODrawing Normals to Surfaces
 

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  1. PODrawing Normals to Surfaces
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    <p>I am trying to draw the normal vectors to a mesh file so I can see how the normal vectors bounce from their respected face. In the draw function, it takes in each face and draws a line from the center point of the face to the (center + normal vector). When I run it, however, I do not see any red lines bouncing off each face. What am I doing wrong here?</p> <pre><code>void drawTria(myFace face) { glNormal3f((face.getNormal().x), (face.getNormal().y), (face.getNormal().z)); wired ? glBegin(GL_LINE_LOOP) : glBegin(GL_POLYGON); glColor3f(0.0, 0.0, 0.5); glVertex3f(vertexList.at(face.v1-1).x, vertexList.at(face.v1-1).y, vertexList.at(face.v1-1).z); glVertex3f(vertexList.at(face.v2-1).x, vertexList.at(face.v2-1).y, vertexList.at(face.v2-1).z); glVertex3f(vertexList.at(face.v3-1).x, vertexList.at(face.v3-1).y, vertexList.at(face.v3-1).z); glEnd(); // Drawing normals glBegin(GL_LINES); glColor3f(1.0, 0.0, 0.0); glVertex3f(face.getCenter().x, face.getCenter().y, face.getCenter().z); glVertex3f((face.getCenter().x+face.getNormal().x), (face.getCenter().y+face.getNormal().y), (face.getCenter().z+face.getNormal().z)); glEnd(); } myVertex myFace::getCenter() { myVertex center; center.x = (vertexList.at(v1-1).x + vertexList.at(v2-1).x + vertexList.at(v3-1).x)/3; center.y = (vertexList.at(v1-1).y + vertexList.at(v2-1).y + vertexList.at(v3-1).y)/3; center.z = (vertexList.at(v1-1).z + vertexList.at(v2-1).z + vertexList.at(v3-1).z)/3; return center; } myVertex myFace::getNormal() { myVertex normal; normal.x = ((vertexList.at(v2-1).y - vertexList.at(v1-1).y) * (vertexList.at(v3-1).z - vertexList.at(v1-1).z)) - ((vertexList.at(v2-1).z - vertexList.at(v1-1).z) * (vertexList.at(v3-1).y - vertexList.at(v1-1).y)); normal.y = ((vertexList.at(v2-1).z - vertexList.at(v1-1).z) * (vertexList.at(v3-1).x - vertexList.at(v1-1).x)) - ((vertexList.at(v2-1).x - vertexList.at(v1-1).x) * (vertexList.at(v3-1).z - vertexList.at(v1-1).z)); normal.z = ((vertexList.at(v2-1).x - vertexList.at(v1-1).x) * (vertexList.at(v3-1).y - vertexList.at(v1-1).y)) - ((vertexList.at(v2-1).y - vertexList.at(v1-1).y) * (vertexList.at(v3-1).x - vertexList.at(v1-1).x)); return normal; } </code></pre>
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    1. COCreate a "model" consisting of a single triangle (0,0)(1,0)(0,1) and make sure your normal is the expected (0,0,1) and your center point is appropriate.
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    2. COYou could also consider simplifying your code. It is difficult to read, and performs far too many operations for your simple task - like do not call getCenter 6 times when only one is needed, etc.
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    3. COLike genpfault said, reduce it down to simpler problems: does getNormal() produce the right answer for a simple case? does getCenter()? You could also print out the vertices under `// drawing normals` and see whether the first point is the same as the second point.
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