View Full Version : Parallax mapping troubles :(

02-09-2004, 02:16 AM
I've been experimenting with parallax, maping yesterday, but faced some problems.

What I've been doing was:
1st: gluLookAt
2nd: draw geometry stage + passing tangent, binormal, normal to vp
3rd: passing eyepos, + MVP,MV,MVIT matrices to cg vp
4th: cg vp -> mul(mvit,eyepos), E=eyepos-IN.pos, mul(TBN, E)
5th: cg fp, fetch height from texture, normalize E, use the function to calculate offset offset=(h*E.xy/E.z)
The problem seems to be connected with transformations, as the texture appears to rotate vhen crossing some point (moving with gluLookAt)

02-09-2004, 07:07 AM
Moving to the Advanced forum.

02-09-2004, 08:45 AM
Is MVIT the inverse-transpose? I thought it should be simply inverce. But MVI*eye is always (0, 0, 0). I don't know if this can help, but...

02-09-2004, 09:23 AM
Whoups, yes you're right :eek: must start coding more carefully.

Now it's only sharp angle artifacts to get rid of http://www.opengl.org/discussion_boards/ubb/frown.gif
I'll have to sit a while to translate fp code to Cg, unfortunately I mised good ol' assembly http://www.opengl.org/discussion_boards/ubb/frown.gif But docs rely on it...

Hope vp is correct now:

struct a2v
float4 Position : POSITION;
float2 TexCoord0 : TEXCOORD0;

struct v2f
float4 HPosition : POSITION;
float2 TexCoord0 : TEXCOORD0;
float3 Eye : TEXCOORD1;

v2f main(a2v IN,
uniform float4x4 ModelViewProj,
uniform float4 EyePos,
uniform float4 T,
uniform float4 B,
uniform float4 N
v2f OUT;

OUT.HPosition = mul(ModelViewProj, IN.Position);
OUT.TexCoord0 = IN.TexCoord0;

float3x3 TBN = float3x3(T.xyz, B.xyz, N.xyz);
float3 E = EyePos.xyz-IN.Position.xyz;
E = mul(TBN, E);

OUT.Eye = E;

return OUT;

[This message has been edited by M/\dm/\n (edited 02-09-2004).]

02-09-2004, 09:39 AM
Well, I also wrote a parallax mapping app (about 5 minutes ago) and so far i can see, my vp looks exact ys yours one.
Are you drawing some sort of patch? This would explain your static TBN vectors http://www.opengl.org/discussion_boards/ubb/biggrin.gif

02-09-2004, 10:06 AM
Yup, right now I'm trying to sort things out on plane, then I'll go into 3D + I think I'll pass only 2 of 3 TBN vectors to GPU, 3rd will be cross on GPU (gonna see how FX5200 will handle that). And I've learned that uniform parameters are real pain in a** when you have 10+ shaders in one app.

[This message has been edited by M/\dm/\n (edited 02-09-2004).]

02-10-2004, 01:39 AM
Huh, I think I've finally got algo working http://www.opengl.org/discussion_boards/ubb/smile.gif

But I noticed that there are prety ugly artifacts when parallax is applied on some of my textures:
W/O parallax
W parallax
Tried experimenting with biases, but that doesn't seem to be a good solution, as you'll have flaws or no parallax http://www.opengl.org/discussion_boards/ubb/frown.gif
Of course my textures arn't very nice as they have a lot of sharp angles.

BTW, cg fp:

void main(float2 TexCoord0 : TEXCOORD0,
float3 Eye : TEXCOORD1,

out float4 color : COLOR,

uniform sampler2D diffuseMap,
uniform sampler2D heightMap
float3 height = tex2D(heightMap, TexCoord0).xyz*0.04-0.02;

float4 tmpcol = tex2D(diffuseMap, TexCoord0+(height*Eye.yx));

float3 C = tmpcol.xyz*tmpcol.w;
color.xyz = C;
color.w = 1;

I'm storing lightmap in alpha of diffuse map. Still can't understand why I had to swap Eye.xy to Eye.yx.