diff options
| -rw-r--r-- | progs/redbook/stencil.c | 21 |
1 files changed, 19 insertions, 2 deletions
diff --git a/progs/redbook/stencil.c b/progs/redbook/stencil.c index 5626d55be6..b33e40a030 100644 --- a/progs/redbook/stencil.c +++ b/progs/redbook/stencil.c @@ -43,6 +43,21 @@ * of the scene. Within this mask, a different model * (a sphere) is drawn in a different color. */ + +/* + * !!! NOTE !!! + * + * This demo is poorly written. The stencil buffer should be + * redrawn in display(), not in the myReshape() function. + * The reason is if the window gets "damaged" then the stencil buffer + * contents will be in an undefined state (myReshape is not called when + * a window is damaged and needs to be redrawn). If the stencil buffer + * contents are undefined, the results of display() are unpredictable. + * + * -Brian + */ + + #include <stdlib.h> #include <GL/glut.h> @@ -90,6 +105,8 @@ void display(void) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); + glStencilOp (GL_KEEP, GL_KEEP, GL_KEEP); + /* draw blue sphere where the stencil is 1 */ glStencilFunc (GL_EQUAL, 0x1, 0x1); glCallList (BLUEMAT); @@ -97,7 +114,6 @@ void display(void) /* draw the tori where the stencil is not 1 */ glStencilFunc (GL_NOTEQUAL, 0x1, 0x1); - glStencilOp (GL_KEEP, GL_KEEP, GL_KEEP); glPushMatrix(); glRotatef (45.0, 0.0, 0.0, 1.0); glRotatef (45.0, 0.0, 1.0, 0.0); @@ -110,6 +126,7 @@ void display(void) glPopMatrix(); glFlush(); + glutSwapBuffers(); } /* Whenever the window is reshaped, redefine the @@ -164,7 +181,7 @@ key(unsigned char k, int x, int y) int main(int argc, char** argv) { glutInit(&argc, argv); - glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH | GLUT_STENCIL); + glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH | GLUT_STENCIL); glutInitWindowSize (400, 400); glutCreateWindow (argv[0]); myinit (); |