Using libisfast

Using libisfast

The libisfast library is a set of demonstration routines that show how libpdb can be used to measure and maintain OpenGL performance data. libisfast is based on purely subjective performance criteria. If they're appropriate for your application, feel free to use them. If not, copy the source code and modify it accordingly.

In all cases that follow, the term "triangles" refers to a triangle strip with 37 vertices. The triangles are drawn with perspective projection, lighting, and smooth (Gouraud) shading. Unless otherwise stated, display-list-mode drawing is used. (This makes isfast yield more useful results when the target machine is being accessed over a network.)

The application must initialize isfast before performing any performance measurements, and clean up after the measurements are finished. On X11 systems these tasks are accomplished by calling

int IsFastXOpenDisplay(const char* displayName);

and

void IsFastXCloseDisplay(void);

respectively. IsFastOpenXDisplay() returns zero if the named display could not be opened, and nonzero if the display was opened successfully.

DepthBufferingIsFast() returns nonzero if depth buffered triangles can be drawn at least one-half as fast as triangles without depth buffering:

int DepthBufferingIsFast(void);

ImmediateModeIsFast() returns nonzero if immediate-mode triangles can be drawn at least one-half as fast as display-listed triangles:

int ImmediateModeIsFast(void);

Note that one significant use of ImmediateModeIsFast() may be to decide whether a "local" or a "remote" rendering strategy is appropriate. If immediate mode is fast, as on a local workstation, it may be best to use that mode and avoid the memory cost of duplicating the application's data structures in display lists. If immediate mode is slow, as is likely for a remote workstation, it may be best to use display lists for bulky geometry and textures.

StencillingIsFast() returns nonzero if stencilled triangles can be drawn at least one-half as fast as non-stencilled triangles:

int StencillingIsFast(void);

TextureMappingIsFast() returns nonzero if texture-mapped triangles can be drawn at least one-half as fast as non-texture-mapped triangles:

int TextureMappingIsFast(void);

Although the routines in libisfast are useful for a number of applications, you should study them and modify them for your own use. That way you'll explore the particular performance characteristics of your systems: their sensitivity to triangle size, triangle strip length, culling, stencil function, texture-map type, texture-coordinate generation method, and so on.