OpenGL Display Lists A way to improve performance.

Why Use Display Lists May improve performance. You can define the geometry and/or state changes once and execute them multiple times. Download remotely to reduce network overhead. Even locally, you can reduce overhead by storing frequently used commands.

EXAMPLE Consider a Tricycle. Two same sized wheels. –Offset from one another. One larger wheel. –Also offset. Use ONE wheel description in a display list and execute the list three times.

OpenGL Code GLuint theTorus; theTorus = glGenLists(1); glNewList(theTorus, GL_COMPILE); torus(8,25); /* draw the torus */ glEndList();... (and in display function) glClear(GL_COLOR_BUFFER_BIT); glColor3f(1.0, 1.0, 1.0); glCallList(theTorus); glFlush();

OpenGL Code GLuint theTorus; theTorus = glGenLists(1); glNewList(theTorus, GL_COMPILE); torus(8,25); /* draw the torus */ glEndList();... (and in display function) glClear(GL_COLOR_BUFFER_BIT); glColor3f(1.0, 1.0, 1.0); glCallList(theTorus); glFlush();

OpenGL Code GLuint theTorus; theTorus = glGenLists(1); glNewList(theTorus, GL_COMPILE); torus(8,25); /* draw the torus */ glEndList();... (and in display function) glClear(GL_COLOR_BUFFER_BIT); glColor3f(1.0, 1.0, 1.0); glCallList(theTorus); glFlush();

OpenGL Code GLuint theTorus; theTorus = glGenLists(1); glNewList(theTorus, GL_COMPILE); torus(8,25); /* draw the torus */ glEndList();... (and in display function) glClear(GL_COLOR_BUFFER_BIT); glColor3f(1.0, 1.0, 1.0); glCallList(theTorus); glFlush();

OpenGL Code GLuint theTorus; theTorus = glGenLists(1); glNewList(theTorus, GL_COMPILE); torus(8,25); /* draw the torus */ glEndList();... (and in display function) glClear(GL_COLOR_BUFFER_BIT); glColor3f(1.0, 1.0, 1.0); glCallList(theTorus); glFlush();

Not Guaranteed Although you’re not guaranteed that your OpenGL implementation optimizes display lists for any particular uses, executing display lists is no slower than executing the commands contained within them individually. There is some overhead in jumping to a display list.

Optimization Possibilities Matrix Operations. Compute both the matrix and its inverse and store in a display list. Raster bitmaps and images. Transform the data into a representation preferred by the hardware and store in a display list. Lights, Material Properties, and Lighting Models. Put material definitions in a display list. Polygon stipple patterns.

Store State Settings with Geometry glNewList(1, GL_COMPILE); Draw_some_geometric_objects(); glEndList(); glLoadMatrix(M); glCallList(1); glNewList(1, GL_COMPILE); glLoadMatrix(M); Draw_some_geometric_objects(); glEndList()’ glCallList(1);

What’s Stored in a Display List Only the values for expressions. If values in an array are subsequently changed, the display list values DON’T change!

Cannot Be Stored glAreTexturesResident() glClientActiveTexture() glColorPointer() glDeleteLists() glDeleteTextures() glDisableClientState() glEdgeFlagPointer() glEnableClientState() glFeedbackBuffer() glFinish() glFlush() glFogCoordPointer() glGenLists() glGenTextures() glGet*() glIndexPointer() glInterleavedArrays() glIsEnabled() glIsList() glIsTexture() glNormalPointer() glPixelStore() glPopClientAttribute() glPushClientAttribute() glReadPixels() glRenderMode() glSecondaryColorPointer() glSelectBuffer() glTexCoordPointer() glVertexPointer()

Hierarchical Display Lists A list that executes another display list by calling glCallList() between a glNewList() and glEndList() pair. A default limit to the nesting level of 64. glGetIntegerv(GL_MAX_LIST_NESTING, GLint * data); (for your implementation)

Redbook Examples torus.c list.c stroke.c