Screen Space Ambient Occlusion

After implementing directional shadow mapping and improving shadow controls in the editor, the nextstep was to add another important lighting feature to the engine: Screen Space Ambient Occlusion.

The goal of this update was to improve contact shadows and depth perception in the scene by darkening small creases, intersections and areas where geometry is close together.

Unlike shadow mapping, SSAO is not generated from a light source. Instead, it works in screen spaceusing the camera depth and normal information. This makes it a good complement to the existinglighting system, especially for adding subtle occlusion around objects, corners and concave shapes.

https://www.youtube.com/watch?v=JbKP1FUOFG4

What I Added

For this first SSAO implementation, I added a full rendering path dedicated to ambient occlusion.

The system now includes:

• SSAO geometry pass

• SSAO depth buffer

• SSAO normal buffer

• SSAO raw occlusion texture

• SSAO blur pass

• SSAO integration in the lighting shader

• Scene-level SSAO settings

• Editor controls in Scene Configuration

• Serialization support for SSAO settings

This turns SSAO into a proper configurable scene feature instead of a hardcoded renderer experiment.

SSAO Geometry Pass

The first step was to create a dedicated geometry pass for SSAO.

This pass renders the visible scene into two separate buffers:

• Depth

• View-space normals

The depth buffer is used to reconstruct the position of each pixel in view space. The normal buffer isused to orient the SSAO sampling hemisphere around the surface direction.

The pass supports both static meshes and skinned meshes, following the same vertex buffer selection logic used by the main mesh rendering pass.

This is important because animated characters and CPU/GPU skinned meshes also need to contribute correctly to the ambient occlusion result.

SSAO Sampling

Once depth and normals are available, the SSAO pass runs as a fullscreen pass.

For each pixel, the shader reconstructs its view-space position using the depth value and the inverse projection matrix. Then it samples a small kernel of points around that position, oriented around thepixel normal.

If nearby samples are found to be closer than expected, the pixel receives more occlusion.

The result is written into an SSAO texture where:

• White means no occlusion

• Grey or black means stronger occlusion

This gives the renderer a screen-space mask that can later be used in the lighting pass.

Noise Reduction and Randomized Sampling

A basic SSAO kernel can easily produce visible banding or repeated patterns.

To reduce this, I added per-pixel randomization using Interleaved Gradient Noise. This rotates thetangent space used by the sample kernel and helps break up visible patterns across the screen.

The SSAO shader also includes range checking and bias controls to reduce false occlusion and avoidexcessive darkening on unrelated surfaces.

The main tunable values are:

• Radius

• Bias

• Strength

• Sample Count

These values have a strong impact on the final look. A larger radius makes the effect visible over a widerarea, while a smaller bias makes contact occlusion easier to detect.

SSAO Blur Pass

The raw SSAO result is intentionally noisy because it uses a limited number of samples per pixel.

To clean it up, I added a separate blur pass.

The blur pass reads from the raw SSAO texture and writes into a blurred SSAO texture. The lighting passthen uses the blurred version by default.

This makes the final result much smoother and more stable while keeping the SSAO pass relatively simple.

For debugging, it is still possible to disable the blur and inspect the raw SSAO result directly.

Lighting Integration

After generating the SSAO texture, I connected it to the main lighting shader.

The SSAO value is sampled using screen-space coordinates and is applied to the ambient or indirectlighting contribution.

This means SSAO does not behave like a normal shadow from a light. Instead, it reduces indirectlighting in areas where nearby geometry blocks ambient light.

This makes the effect more physically reasonable and avoids treating SSAO as if it belonged to a specificlight component.

Result

This update adds a complete first version of Screen Space Ambient Occlusion.

The engine can now:

• Generate SSAO depth and normal buffers

• Compute a screen-space ambient occlusion mask

• Apply randomized hemisphere sampling

• Blur the SSAO result

• Use SSAO in the main lighting shader

• Enable or disable SSAO from the editor

• Toggle debug view

• Tune radius, bias, strength and sample count

This makes the lighting pipeline more complete and gives scenes better contact definition, especially around intersections, corners and small concave areas.

The next improvements would likely be a bilateral blur, half-resolution SSAO, and depth-linearized comparisons.