Why this GLSL code don't work on old Intel card (openGL 2.1)? -

as know, 3d software has xyz-axis in view section. suppose draw coordinate axis that. here method.

firstly, there function named drawoneaxis() used draw 1 axis. invoke 3 times. however, everytime before draw axis, change model matrix can 3 axes perpendicular each other. function changeuniform_mvp() do.

void draw() {     (int = 0; < 3; i++)  // 0 - x axis, 1 - y axis, 2 - z axis     {         changeuniform_mvp(i);         drawoneaxis();     } } 

vertex shader:

#version 110  uniform mat4 mvp;  void main() {     gl_position = mvp * gl_vertex; } 

in function init(), shader compiled , linked , program id named programid. @ end of init(), use shader invoke gluseprogram(programid).

the result on 2 computers:

pc 1: intel card, opengl 3.1, pc 2: intel card, opengl 2.1, 1 axis drew (z axis) 

why 2 different results here?
1 magic thing!!! result correct on pc2 after add 2 lines of code function draw().

void draw() {     (int = 0; < 3; i++)     {         gluseprogram(programid);  // 1         changeuniform_mvp(i);         drawoneaxis();         gluseprogram(0);  // 2     } } 

it seems must reset program every time draw something. think unnecessary because use same shader draw things. i'm confused this.

is bug of old intel card's driver? why ok after add 2 lines of code?

hard answer. older intel opengl drivers have issues.

drawthreeaxes() perhaps?