Multiple sequentual glPushAttrib/glPopAttrib incorrect behaviour

Question

#include <GL/glut.h>

void reshape(int w, int h){
  glViewport(0, 0, w, h);
  
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D(-w/2, w - w/2, -h/2, h - h/2);
  
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

void display(){
  glClear(GL_COLOR_BUFFER_BIT);
  
  glColor3f(1, 1, 1);
  
  glPushAttrib(GL_ALL_ATTRIB_BITS);
  glColor3f(1, 0, 0);
  glPopAttrib();
  
  glRecti(0, 0, 10, 10); // draws white rect
  
  // Commenting the line makes next rect white
  // Uncommenting the line makes next rect red
  glTranslatef(0, 0, 0);
  
  glPushAttrib(GL_ALL_ATTRIB_BITS);
  glColor3f(1, 0, 0);
  glPopAttrib();
  
  glRecti(20, 20, 30, 30); // draws white or red rect
  
  glutSwapBuffers();
}

int main (int argc, char * argv[]){
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA);
  
  glutInitWindowSize(800, 600);
  glutCreateWindow("OpenGL lesson 1");
  
  glutReshapeFunc(reshape);
  glutDisplayFunc(display);
  
  glutMainLoop();
  
  return 0;
}

The code above is full compilable programm that renders two rectangles. The programm produce different results depending on weather line "glTranslatef(0, 0, 0);" commented or not. Is that a bug, or misusage of OpenGL?

Answer 1

Is that a bug, or misusage of OpenGL?

That is just a bug. The spec clearly states that glColor will set the current RGBA color value, which will become the vertex's color the next time a vertex is formed. This would happen by the next glVertex call inside a glBegin/glEnd block. glRect is specified to be equivalent to glBegin(); glVertex() [4x]; glEnd().

The current RGBA color value is part of the GL_CURRENT_BIT attribute group, and is of course included in GL_ALL_ATTRIB_BITS. glTranslate is to only affect the top element of the currenttly selected matrid stack. The correct output for this code are two wihite rectangles, no matter if a glTranslate is there or not.

However, all this stuff is horribly outdated, and deprecated since 2008.