Hardware limitation reached, can only emit 78 vert

OpenGL
1

Hello. In the context of school I wanted to write a simple program that using the geometry shader will generate a 32x32 pixel terrain.
Unfortunately, when linking the program Shader, I read the following error in my log:


Loading GL_ARB_fragment_shader ext.     SUCCESS
Loading GL_ARB_vertex_shader ext.       SUCCESS
Loading GL_ARB_geometry_shader4 ext.    SUCCESS
Loading GL_ARB_shader_objects ext.      SUCCESS

Creating program object: "program1"
Compiling vertex shader:                SUCCESS
Compiling fragment shader:              SUCCESS
Compiling geometry shader:              SUCCESS
GL_MAX_GEOMETRY_OUTPUT_VERTICES_EXT:    1024
Linking program shader:                 FAILED
printProgramInfoLog: Geometry info
-------------
(0) : error C6033: Hardware limitation reached, can only emit 78 vertices of this size

GL_MAX_TEXTURE_UNITS_ARB:    4
OpenGL version: 3.3.0

I’ve lost many hours to find something about it …
The maximum number of vertices emitted is 1024, so why there is 78?
I would be very grateful if someone help me to understand it.

this is my geometry sahder:


#version 150
#extension GL_EXT_geometry_shader4 : enable

uniform sampler2D heightmap;

in vec3 vlight[3];
in vec3 vnormal[3];
in vec3 vpoint[3];
out vec3 light;
out vec3 normal;
out vec3 point;


void main()
{
   int i,u,v;
   vec4 vertex;
   vec2 texture_coord;
   vec4 texture_color;

for(i=0; i<32; i++)
for(u=0; u<32; u++)
{
   texture_coord.x = i;
   texture_coord.y = u;
   texture_color = texture2D(heightmap, texture_coord);
   vertex.x = -1+i*0.1;
   vertex.y = -1+u*0.1;
   vertex.z = -1;
   vertex.w = 1;
   gl_Position = vertex;
   gl_PointSize = 0;

   light = vlight[0];
   normal = vnormal[0];
   point = vpoint[0];
   EmitVertex();

   texture_coord.x = i+1;
   texture_coord.y = u;
   texture_color = texture2D(heightmap, texture_coord);
   vertex.x = -1+(i+1)*0.1;
   vertex.y = -1+u*0.1;
   vertex.z = 0;
   vertex.w = 1;
   gl_Position = vertex;
   //gl_PointSize = 0;
   light = vlight[1];
   normal = vnormal[1];
   point = vpoint[1];
   EmitVertex();

   texture_coord.x = i;
   texture_coord.y = u+1;
   texture_color = texture2D(heightmap, texture_coord);
   vertex.x = -1+i*0.1;
   vertex.y = -1+(u+1)*0.1;
   vertex.z = 0;
   vertex.w = 1;
   gl_Position = vertex;
   //gl_PointSize = 0;
   light = vlight[2];
   normal = vnormal[2];
   point = vpoint[2];
   EmitVertex();
   EndPrimitive();
   
}


}

When in loop i change from:
“i<32” and “u<32”
to:
“i<4” and “u<4”
there are 443 = 48 vertives and all is OK.

Screen of my 16 triangles:

my graphics card: Gainward GeForce 8400GS 512MB

2

Looky here:


out vec3 light;
out vec3 normal;
out vec3 point;
out vec4 gl_Position; // exists already

This takes 13 float slots.
13 * 78 = 1014.

It may be an error that 1024 “vertices” are reported as the limit, while it’s 1024 floats. Or maybe with certain data-formats for gl_Position the vtxcount of 1024 could actually be reached.

3

I can continue to generate only 204 vertices.

Is there any way to increase the number of vertices?

4

Reduce the amount of data stored per-vertex.

5

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