I am attempting to light a square. The square is made up of 4 vertices having a position and a normal. The normal for all the vertices is pointing towards the user(0.0f, 0.0f, -1.0f). I have applied a material with the diffuse and ambient color set to Red.
I am using a directional light which has a direction of (0.0f, 0.0f, 1.0f). If I set the diffuse color to White, the square shows up Red as I would expect. If I change the color to something else, like Blue, the square appears black where I was expecting it to be purple.
The reason for this line "d3dDevice.Lights[0].LightType = (LightType)3;" is that the CLR 2.0 version of MDX does not have LightType enumeration defines with Directional, Spot, or Point.
private void SetupLights() { ColorValue val = new ColorValue(Color.Red.R, Color.Red.G, Color.Red.B); Material m = new Material(); |
Lighting Question/Problem
LucyS
Setting your material's diffuse to be RED is stating that it will *reflect* the red wavelengths and *absorb* the others. Setting your light to be BLUE is stating that it is contributing blue wavelengths from its source.
BLUE wavelengths being (0,0,1) do not contain any red (1,0,0) - thus the material, by definition, is absorbing the incoming light energy and reflects nothing - which is black (0,0,0). Setting the diffuse to WHITE (1,1,1) says it'll reflect all incoming wavelengths, hence you get the colour you're expecting.
In the real-world there aren't many occurences of "pure" colour (such as appears in computer graphics) - which is why you might be expecting to see a combination of blue and red being purple (which, in CG is an additive operation not muliplicative).
Might be worth picking up a graphics text on the subject - I recently read Advanced Lighting and Materials with Shaders that covers this sort of thing reasonably well. I'd imagine many other books do a good job.
hth
Jack