Common Bottlenecks
Entry posted by Josh ·
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Leadwerks 4.3 brings a big performance boost to your games. In this blog I am going to talk about some of the common problems you can eliminate to make your games run faster.
When slow performance is encountered, it is typically one really bad mistake that is slowing everything down. Here's a few common bottlenecks for performance you can create in your games, how to identify them, and how to fix them.
Shadow Updates
Shadow rendering is cheaper than regular renders because no textures have to be used, but extra rendering passes to update shadows can add up.
How to identify: The game stats will display the number of shadows updated. If this is more than a few, you might have a problem. Remember that point lights require six extra passes, and directional lights three, but both only count as one shadow. You also want your rendered shadow polys to be as low as possible.
How to fix: Figure out what objects are triggering the redraw and whether it is necessary. Non-moving high-polygon models should use the static shadow mode so they don't have to be redrawn during a render. In version 4.3, low and medium light quality settings will also stagger shadow updates so that fewer are rendered each frame. (This can also make it harder to detect a problem, so maybe test on high quality settings when you are examining this.)
GPU Pixel Pipeline
The GPU has a limited number of stream processors it can split up the task of rendering an image with. When you overload the GPU pixel pipeline it slows down your program.
How to identify: If you have a much higher framerate at a lower screen resolution, this is probably the cause.
How to fix: Lower light quality settings, remove post-processing effects, or run at a lower screen resolution.
GPU Vertex Pipeline
This is pretty rare because the number of vertices the GPU has to process are tiny compared to the number of pixels, but it is possible.
How to identify: Slow speed regardless of screen resolution, slow even when rendering the scene with no gameplay, extremely high-polygon counts in the game stats (like 2,000,000+). There are some applications where extremely high polygon counts are acceptable, but unless you are specifically making such an application and are aware of this, it probably means you should use models designed for real-time games.
How to fix: Use lower-resolution models or lighten up on the vegetation.
Too Many Objects
The renderer itself has a cost of computation on the CPU. The more separate objects there are, the more the CPU has to work to determine what objects are visible. On the other hand, discarding large numbers of objects can give a big speed boost, so it's always a balance.
How to identify: The render time shown in your game stats will be more than a few milliseconds, and the number of batches, displayed in the game stats, will be very high. It's all relative but if you have a simple scene and 500 batches are being drawn, there is probably a problem. Large spread out maps with dense distribution of objects can often have this problem. This will happen on all machines, regardless of how good the GPU is. The most complex maps I've ever made had about 700 batches rendered. There is no need to go above that no matter how big the map is, because objects in the distance will be culled. The vegetation system does not cost much on a per object basis, so it is an extremely efficient way to lay down a lot of dense objects.
How to fix: Use the model editor Collapse feature to collapse models into a single object and resave them. Also set the view range of smaller objects to a closer distance so there are fewer of them visible in the distance.
Slow Collision
If your game slows down when you get close to an object, you might have a high-poly collision mesh.
How to identify: The physics update time in the game stats will be more than a few milliseconds. Enable "View Physics" in the editor and check to make sure all physics shapes are low-poly.
How to fix: Use the model editor to generate a low-poly physics shape with the best available option.
Code Errors
Is your game constantly reloading files from the hard drive? Are you performing lots of pick operations each frame? Did you create a runaway loop of new objects to process?
How to identify: Comment out sections of your code and test the framerate.
How to fix: Figure out the main section that is causing the slowdown, then keep commenting out smaller and smaller parts until you narrow down the problem. Post on the forum if you don't know why something is causing a performance drop.
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