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The pseudo code to implement parallax mapping is the following :

float parallaxHeight = 0.035f
float height = tex2D ( HeightMap ).r;
float offset = parallaxHeight * ( 2.0f * height - 1.0f);
float2 parallaxTexCoord = texCoord + offset * viewVec.xy;

The height is a value between 0 and 1 but the offset is a value in the range [-parallaxHeight, +parallaxHeight]. The reason for this mapping is to distribute the distortion of the texture map equally in 2 directions.

attribute vec3 rm_Binormal;
2

attribute vec3 rm_Tangent;
3

varying vec3 vCameraDir;
5

void main( void )
7

{
8

gl_Position = ftransform();
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gl_TexCoord[0] = gl_MultiTexCoord0;
10

vec4 view_position = gl_ModelViewMatrix * gl_Vertex;
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vec3 camera_dir = normalize(view_position.xyz);
13

mat3x3 TangentSpace;
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TangentSpace[0] = gl_NormalMatrix * rm_Tangent;
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TangentSpace[1] = gl_NormalMatrix * rm_Binormal;
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TangentSpace[2] = gl_NormalMatrix * gl_Normal;
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vCameraDir = camera_dir * TangentSpace;
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// equal to

.
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//vCameraDir.x = dot(camera_dir, TangentSpace[0]);
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//vCameraDir.y = dot(camera_dir, TangentSpace[1]);
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//vCameraDir.z = dot(camera_dir, TangentSpace[2]);
24

}

varying vec3 vCameraDir;
2

uniform sampler2D DiffuseMap;
4

uniform sampler2D HeightMap;
5

uniform float fHeight;
7

void main( void )
9

{
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vCameraDir = normalize(vCameraDir);
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vec3 texcoord = vec3(gl_TexCoord[0].xy, fHeight);
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float depth = (2.0*texture2D(HeightMap, texcoord).r-1.0) *fHeight;
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vec3 texcoord_corrected = texcoord + vCameraDir.xyz * depth;
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gl_FragColor = texture2D(DiffuseMap, texcoord_corrected.xy);
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}

http://knol.google.com/k/shader-fx-parallax-mapping#
http://www.ownself.org/oswpblog/?p=59
http://blog.csdn.net/soilwork/article/details/1452437

posted on 2012-04-07 17:03 情絕格調(diào)(fresmaster) 閱讀(1359) 評(píng)論(0) 編輯收藏引用所屬分類: Graphics 、Coding

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相關(guān)文章: glAlphaFunc in OpenGL ES2.0 Gamma Correction Hemi-Sphere Lighting Light Mapping GLSL.Ambient occlusion GLSL.High Dynamic Range GLSL.Depth Of Field GLSL.Image post-processing GLSL.Parallax mapping GLSL.Refract & Reflect & Diffraction

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