Re: Is there a way to get OpenGL to do linear texture-mapping?

• Subject: Re: Is there a way to get OpenGL to do linear texture-mapping?
• From: Nicholas Francis <email@hidden>
• Date: Wed, 30 Mar 2005 14:08:24 +0200
• Delivered-to: email@hidden
• Delivered-to: email@hidden

struct appdata {
	float4 vertex;
	float3 normal;
	float2 texcoord;
};

v2f vert(appdata v) {
	v2f o;
	// HACK FOR OCEAN WATER: fade out waves...
	waveHeights *= v.texcoord.x;
	o.col.a = v.texcoord.y;

	o.pos = mul(glstate.matrix.mvp, v.vertex.xyzw);
	o.fog = o.pos.z;

	// Calculate the reflection vectors
	// ------------------------------------------------
	// basics: Get the screenspace UV coords
	// TODO: normal-based pertubation
	float4x4 mat= float4x4 (
		128,0,0,128,// - _BumpPeturb / 4,
		0,-128,0,128,// - _BumpPeturb / 4,
		0,0,.5,.5,
		0,0,0,1
	);
	o.ref = mul (mat, o.pos);
}

On Mar 30, 2005, at 1:42 PM, jonas echterhoff wrote:

No, that doesn't make a difference. I don't think that most modern OpenGL implementations would benefit performance-wise from affine texture-mapping, since it's all in hardware.
Using glTexGen with GL_EYE_LINEAR should probably use linear texture-mapping i guess. I cannot use that, however, since I'm using a vertex shader and can't use the TexGen stuff that way. But it should be possible somehow.. Maybe by manipulating the projection and/or texture matrix?

jonas

On Mar 30, 2005, at 12:16 PM, Dario Accornero wrote:

On 30 Mar 2005, at 10:38, jonas echterhoff wrote:

I'm looking for a way to get OpenGL to draw a texture with linear/affine mapping and not perspective correct. The reason is that i want to render a reflection of a part of my scene. This reflection is rendered to a texture, so it is already perspective correct. If I render this reflection texture using perspective-correct texture mapping it will end up looking distorted.

Assuming this is fixed-function, I'm not sure there's a way to *force* affine mapping, but... have you tried glHint(GL_PERSPECTIVE_CORRECTION_HINT,GL_FASTEST) right after glBindTexture? GL_FASTEST should in theory give you affine mapping, whereas GL_NICEST should always give you perspective mapping, but as you can see it's just a glHint, not a requirement...

HTH,
Dario

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Nicholas Francis
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