As you can see a ~500fps increase is quite significant!

It all boils down to Alpha Clipping materials. Alpha clipping is a technique to make rendering things like plants with lots of branches and leaves without the need for massively complicated meshes.

This is done by sampling the main colour texture for the object in the depth pass and discarding fragments that have an alpha value below a threshold.

This means when the colour pass rolls the branches look like branches and not weird green effects.

The downside to alpha clipping is it requires the fragment shader in the depth only pass and also textures to be bound to the pipeline - it just has more overhead.

When I originally implemented alpha clipping I added the fragment shader to my depth only material to enable the same graphics pipeline to be used for alpha clipping and non-alpha clipping objects.

I originally did this because Vulkan encourages as few graphics pipelines as possible as binding pipelines is an expensive operation.

But as it turns out, running the fragment shader for objects that don't need it incurs major overhead.

So simply, I have created a alpha clipping depth only material and a non-alpha clipping variant that does not have the fragment shader. This required overhauling some of the internal draw command generation to sort objects into alpha clipping/non-alpha clipping queues.

For those interested into the, the alpha clipped objects are drawn after the full opaque objects in the same render pass.

Some other notes, this also improve shadow generation performance majorly espeically for point lights which have to do 6 passes.

A more minor performance improvement is the change from 32-bit (4 bytes) depth textures to 16 bit (2 bytes), halving the size of all depth textures. meaning a 4k point light goes from 400mb to 200mb.

These screenshots show off the point lights and shadows the forward phong renderer can do in addition to the directional light shadow.

All these screenshots are actually from early January and many things have been improved since, the gamma correction in these images is completely wrong for example which is why everything looks so bright

I like the shots of behind the curtains.

Some technical notes, the point shadows are real-time rendered all in a single depth-only pass using a geometry shader and Vulkan's rendering info system to render to all the cubemap for each light. No old school vkframebuffers and vkrenderpasses here :)

The cubemap faces I believe are 4096, they're definitely 32-bit depth format tho which means one cube map is about 100mb and all 10 means nearly a 1gb in video memory just in cubemap textures 😭 this ran pretty poorly as a result tho "baking" them didn't improve performance that much.