Strange GL draw method behavior

Didier Bur · 2 Oct 2008, 16:16

Hi,
Don't know if it has been discussed before but I have found no response to this question:
Why view.draw GL_QUADS always draws the quads with a black color ?

This doesn't work:

view.drawing_color="red"
view.draw_line p1,p4
view.draw GL_QUADS , [p1,p2,p3,p4]
view.draw GL_QUADS, [p5,p6,p7,p8]

line is red but quads are black
Anyone encountered this before ?

jhauswirth · 2 Oct 2008, 19:04

This is just a guess, but polygons need normals to do lighting, so the default normals are probably causing the bad lighting.
Let's say the normals default to 0,0,0- then that would give you a 0,0,0 for color.

Didier Bur · 2 Oct 2008, 20:04

Changing the point's ordering doesn't solve the problem, so it seems not to be a question of normal.
Same goes with GL_TRIANGLES.

jhauswirth · 2 Oct 2008, 22:39

The real question is how do you specify the normals? You're just giving GL_QUADS the vertices.

Didier Bur · 3 Oct 2008, 21:10

Hi,
Nothing specified in the docs concerning normals. Doc is so sparse you know... I guessed that passing points in a counterclockwise order was orienting the normal up (assuming that these points are on an horizontal plane) ?
You can notice that once drawn, quads are visible from both sides. Is the normal useless or am I completely wrong ?