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Problem with getting pixel pos from depth

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Hi, i`m trying to optimize deferred lighting and i have a problem with getting info about pixel pos from depth. Here`s my spot light fragment code(i selected where i m getting position value):
#version 120
#extension GL_ARB_draw_buffers : require
#extension GL_EXT_gpu_shader4 : require

varying vec2 texCoord;
varying vec3 lightPos;
varying vec3 lightColor;
varying vec3 spotDir;
varying vec4 data;//intensinity,fallof,cosCutoff,metalistic

uniform sampler2D normalTex;
uniform sampler2D materialTex;
uniform sampler2D depthBufferTex;

uniform mat4 invMVP;//i m getting inverted value of modelviewmatrix*projmatrix

float intensity;// = 128.0;
float falloff;// = 512.0;
float spotCosCutoff;
float metalicFilter;

void main()
vec3 normal = texture2D( normalTex, texCoord).xyz * 2.0 - 1.0;
vec4 mat = texture2D( materialTex, texCoord);

///////////////////////HERE starts problem///////////////////////////////////////
float depth=texture2D( depthBufferTex, texCoord).x;
vec2 projPosXY = 2. * vec2( texCoord.x, 1. - texCoord.y ) - 1.;
vec4 posSS = vec4( projPosXY.x, projPosXY.y, depth, 1. );
vec4 posWS = posSS*invMVP;
vec3 position=posWS.xyz/posWS.w;
////////////////////////////END of problem/////////////////////////

float dist = distance( lightPos, position);
vec3 lightDir = normalize( lightPos - position);

float spotEffect = dot(spotDir, -lightDir);
dist = 1.0 / (1.0 + dist * dist * falloff);
vec3 dif = max( (dot( lightDir, normal) * dist * intensity),0.0 )*lightColor ;
vec3 spec = vec3(0.0);
gl_FragColor = vec4( dif*mat.rgb + spec, 1.0);


I`d like to get for "position" value like from gl_vertex*gl_modelviewmatrix.
with invMVP i m getting inverted value of modelviewmatrix*projmatrix.
Any ideas whats wrong?

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It didnt help me because person who answer shows how to store in teksture position value. I dont want to do that. I want get position from depth buffer to have less render targets in deferred lighting(for optimize).

If someone shows me sample code with getting pixel from depth would be nice. Than i can see what am i doing wrong in my shader

[Edited by - furrymaster on August 31, 2010 2:57:48 AM]

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