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How do lights work?

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Hi! Well, D3D is definitely more complex than I thought it was!... I keep running into problem after problem. I hope things will calm down a bit once I have more experience... Anyway, here goes... I have an application in which I display a rotating cube. I define my vertexes with the following format:
  const DWORD VERTEX_FORMAT = D3DFVF_XYZ | D3DFVF_NORMAL | D3DFVF_DIFFUSE;
 
My normals are all normalized and my diffuse color is set to blue (r:0, g:0, b:200). If I set lighting off with a call to SetRenderState( D3DRS_LIGHTING, FALSE ); I get a blue rotating cube with no shading, just the same uniform blue on every face of the cube. As far as I know, that is what I should be getting. The problem comes from when I try to add a light to my scene. Here''s what I do:
	m_pDevice->SetRenderState( D3DRS_LIGHTING, TRUE );
	m_pDevice->SetRenderState( D3DRS_AMBIENT, D3DCOLOR_XRGB( 128, 128, 128 ) );

	D3DMATERIAL8 material;
		ZeroMemory( &material, sizeof( material ) );
		material.Diffuse = D3DXCOLOR( 1.0f, 1.0f, 1.0f, 1.0f );
		material.Ambient = D3DXCOLOR( 1.0f, 1.0f, 1.0f, 1.0f );

	m_pDevice->SetMaterial( &material );

	D3DLIGHT8 light;
		ZeroMemory( &light, sizeof( light ) );
		light.Type      = D3DLIGHT_DIRECTIONAL;
		light.Diffuse   = D3DXCOLOR( 1.0f, 1.0f, 1.0f, 0.0f );
		light.Direction = D3DXVECTOR3( 0.0f, -1.0f, 0.0f );

	m_pDevice->SetLight( 0, &light );
	m_pDevice->LightEnable( 0, TRUE );
 
With the above code, my cube is gray instead of blue, but is otherwise identical to what I get with lighting turned off. I was expecting the different faces on my cube to at least be of different shades of gray. A face hit directly by the light should be brighter than one that is on the opposite side, right? Am I missing anything here? Thanks for any advice!

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Nevermind that, I found my error. I was not copying my normals to the vertex buffer! No wonder it didn''t work properly... I''m surprised I didn''t get weirder results than what I was getting.

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If you only use the ambient light, is your quad gray then? I have problems with the ambient light not mixing its colors with the diffuse color of the quad. Does that work for you?

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