OpenGL Display Lists

1
OpenGL Display Lists

• A way to improve performance.

2
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.

3
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.

4
OpenGL Code
GLuint theTorus theTorus glGenLists(1) glNewLi
st(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()
5
OpenGL Code
GLuint theTorus theTorus glGenLists(1) glNewLi
st(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()
6
OpenGL Code
GLuint theTorus theTorus glGenLists(1) glNewLi
st(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()
7
OpenGL Code
GLuint theTorus theTorus glGenLists(1) glNewLi
st(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()
8
OpenGL Code
GLuint theTorus theTorus glGenLists(1) glNewLi
st(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()
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Not Guaranteed

• Although youre 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.

10
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.

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Store State Settings with Geometry
glNewList(1, GL_COMPILE) glLoadMatrix(M) Draw_so
me_geometric_objects() glEndList() glCallList(1
)
glNewList(1, GL_COMPILE) Draw_some_geometric_obje
cts() glEndList() glLoadMatrix(M) glCallList(1
)
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Whats Stored in a Display List

• Only the values for expressions.
• If values in an array are subsequently changed,
  the display list values DONT change!

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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()

14
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)

15
Redbook Examples

• torus.c
• list.c
• stroke.c