KNOWLEDGE IS POWER

Or put another way, without knowing the cause of your framerate issues, you will be stabbing the dark, throwing away heaps of time making “optimisations” which make no significant impact on your framerate.

Incidentally, this is a good read: https://docs.unrealengine.com/latest/INT/Engine/Rendering/PerformanceProfiling/Guidelines/index.html

 

IDENTIFY WHAT

1. Turn on a framerate counter if you have not already done so. If your engine doesn’t have one, use FRAPS.
2. Turn layers off and on to see which assets are affecting your framerate most.
3. Try and pinpoint it to a specific asset if you can. The table below is sorted by likelihood, so this can give you a clue where to start looking.

 

UNDERSTAND WHY

Use the table below to figure out the reason that asset is hurting your framerate. Understand what is written. Google if the description is not sufficient.

 

APPLY RESOLUTION

Now we know what is hurting our frame rate and why, the resolution is usually simple. Apply the proper resolution. Profit.

 

Issue	Description	Common Causes / Diagnosis	Resolution
Overdraw	When a single screen pixel has to be drawn many times. This can occur from bad sorting, or more typically from blend transparency	Foliage (including grass) large-particle VFX like smoke Diagnose: apply an opaque shader to your VFX or blend assets	Favour fewer, more opaque particles Favour alpha test (stencil) where possible Use extra geometry to keep blend geometry tight around the visible part of the texture
Expensive dynamic lighting	In deferred lighting, each light has to essentially “overdraw” onto each screen pixel.In forward lighting, each light has to draw once per object it hits	Large, overlapping lights Many dynamic shadowcasting lights Diagnose: disable shadowcasting or disable lights entirely	Only use shadowcasters where needed Ensure shadow map resolution is only as big as needed Favour smaller lights with sharper falloff If your engine lets you exclude small objects from shadowmap rendering, do this
Fill rate bound (shader cost)	Bulk of a frame is usually spent “colouring in” your pixels. This is a factor of the time it takes for your shader to be computer per pixel. This is usually a result of too many texture samples.	Usually too many texture samples Diagnose: Throw a single-colour shader on the “problem assets” and check framerate Diagnose: Fill the screen with your suspected “problem asset”. it should be worst when filling the screen.	Use as few texture samples as reasonably possible If using multiple same-UV greyscale masks, instead use a multi-channel mask Consider a shader LOD for things like offset/parallax
Transform-bound (geometry cost)	If calculating the position of mesh vertices is taking longer than filling the pixels they pertain to, you are transform-bound.	Usually because of poor LODs Diagnose: Halve frame resolution (ex. 1920×1080 to 1280×720). If framerate is nowhere near doubled, could be this.	Use LODs (important in large levels or “vistas”) Favour static meshes over skinned ones Use a cheaper vertex shader Reduce geometry
Out of memory	If you are out of memory, your engine may try and cope. Coping measures are usually crippling to performance. In other cases, your game will simply crash.	Usually asset textures Sometimes lightmap textures in a big level. Diagnose: Use engine profiling tools to identify what is eating up your memory	Reduce asset texture resolution, compensate using shared tiling detail textures Reduce lightmap resolution (if applicable). Don’t bother reducing geometry, cube map resolution, shadowmap resolutions (these rarely use much texture memory)