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Thread: Newbie OpenGL Geometry shaders

  1. #1
    Junior Member Newbie
    Join Date
    Feb 2011

    Newbie OpenGL Geometry shaders


    I am using opengl v2.0.1.8x.
    I am trying to apply a geometry shader to the rendering procedure.
    The problem is very unusual (I've put a "// ****** Bug here", before the problem codeline)

    Code :
    #version 120 
    #extension GL_ARB_geometry_shader4 : enable
    in vec3 vertWorldPos[3]; 
    in vec3 vertWorldNormal[3]; 
    out vec3 worldNormal; 
    out vec3 worldPos; 
    uniform vec2 WIN_SCALE; 
    out vec3 dist; 
    void main(void) { 
    vec2 sz = WIN_SCALE;
    vec2 tt = gl_PositionIn[0].xy;
    vec2 t2 = vec2(gl_PositionIn[0].w, gl_PositionIn[0].w);
    vec2 p0 = sz * tt / t2;  // ****** Bug here
    tt = gl_PositionIn[1].xy;
    t2 = vec2(gl_PositionIn[1].w, gl_PositionIn[1].w);
    vec2 p1 = (sz * tt) / t2; // ****** Bug here
    tt = gl_PositionIn[2].xy;
    t2 = vec2(gl_PositionIn[2].w, gl_PositionIn[2].w);
    vec2 p2 = (sz * tt) / t2; // ****** Bug here
    vec2 v0 = p2-p1; 
    vec2 v1 = p2-p0; 
    vec2 v2 = p1-p0; 
    float area = abs(v1.x*v2.y - v1.y * v2.x); // ****** Bug here
    dist = vec3(area/length(v0),0,0); // ****** Bug here
    worldPos = vertWorldPos[0]; 
    worldNormal = vertWorldNormal[0]; 
    gl_Position = gl_PositionIn[0]; 
    dist = vec3(0,area/length(v1),0); // ****** Bug here
    worldPos = vertWorldPos[1]; 
    worldNormal = vertWorldNormal[1]; 
    gl_Position = gl_PositionIn[1]; 
    dist = vec3(0,0,area/length(v2)); // ****** Bug here
    worldPos = vertWorldPos[2]; 
    worldNormal = vertWorldNormal[2]; 
    gl_Position = gl_PositionIn[2]; 

    Thing is that it seems that the compilationcan not be applied on any code of line (in the geometry) where I am using the / or * operators...
    Does anyone know what is wrong with that... and how to fix that?
    I checked the version of the opengl I am using, but it seems that this code should work in the earlier versions as well (which I am using, I got quite old legacy "ATI Radeon x1650 GT" card).


  2. #2
    Senior Member OpenGL Lord
    Join Date
    May 2009
    Code :
    #version 120 
    #extension GL_ARB_geometry_shader4 : enable
    in vec3 vertWorldPos[3];

    First, these three statements cannot go together. GLSL 1.20 does not use in/out on global variables, and ARB_geometry_shader4 does not make this syntax legal. ARB_geometry_shader4 and core geometry shader functionality are specified differently. I would tell you how ARB_geometry_shader4 actually works, but:

    I got quite old legacy "ATI Radeon x1650 GT" card
    That card does not support geometry shaders. Of any kind. So it would be useless to explain.

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