Created attachment 129684 [details]
Typical output
Hi,
I am developing a cross-platform application. I have recently found an issue
that is only present when it is tested on a Ubuntu machine. I have managed =
to
find a minimal example that shows the issue as follows:
The vertex shader:
#version 150
in vec2 pos;
void main(void)
{
gl_Position =3D vec4(pos, 0.0, 1.0);
}
The fragment shader:
#version 150
out vec4 outColour;
void main(void)
{
outColour =3D vec4(1.0f, 1.0f, 1.0f, 1.0f);
}
The geometry shader:
#version 150
layout(points) in;
layout(line_strip, max_vertices =3D 13) out;
uniform mat4 vpMatrix;
void main()
{
for(int i =3D 0; i < 13; i++)
{
float polygonAngle =3D (i * 30) + 90.0f;
vec4 vertexPosition =3D vec4((sin(radians(polygonAngle)) * 0.5f) +
gl_in[0].gl_Position.x, (cos(radians(polygonAngle)) * 0.5f) +
gl_in[0].gl_Position.y, 0.0f, 1.0f);
gl_Position =3D vpMatrix * vertexPosition;
EmitVertex();
}
EndPrimitive();
}
The problem occurs when the shader program is used with multiple VBO's. For
example:
3 separate VBO's are created with {-1.0f, 1.0f}, {1.0f, 1.0f}, {1.0f, -1.0f=
} as
the data. Then, for each repaint:
for(int i =3D 0; i < 3; i++)
{
Bind array buffer i.
glDrawArrays(GL_POINTS, 0, 1);
}
This produces strange results for the third polygon (shown in the attached
image Output.JPG).
If tested on a Windows 10 machine (exactly the same hardware) or an OSX
machine, the results are as expected (3 regular polygons with 12 sides).