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Optimize glow and tonemap gather step in the mobile renderer

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Mobile devices are typically bandwidth bound which means we need to do as few texture samples as possible.

They typically use TBDR GPUs which means that all rendering takes place on special optimized tiles. As a side effect, reading back memory from tile to VRAM is really slow, especially on Mali devices.

This commit uses a technique where you do a small blur while downsampling, and then another small blur while upsampling to get really high quality glow. While this doesn't reduce the renderpass count very much, it does reduce the texture read bandwidth by almost 10 times. Overall glow was more texture-read bound than memory write, bound, so this was a huge win.

A side effect of this new technique is that we can gather the glow as we upsample instead of gathering the glow in the final tonemap pass. Doing so allows us to significantly reduce the cost of the tonemap pass as well.
This commit is contained in:
clayjohn
2025-09-01 14:43:37 -07:00
parent 084d5d407e
commit 2e59cb41f4
22 changed files with 1524 additions and 519 deletions
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4
doc/classes/Environment.xml
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@ -143,13 +143,13 @@
<member name="glow_hdr_scale" type="float" setter="set_glow_hdr_bleed_scale" getter="get_glow_hdr_bleed_scale" default="2.0">
The bleed scale of the HDR glow.
</member>
<member name="glow_hdr_threshold" type="float" setter="set_glow_hdr_bleed_threshold" getter="get_glow_hdr_bleed_threshold" default="1.0">
<member name="glow_hdr_threshold" type="float" setter="set_glow_hdr_bleed_threshold" getter="get_glow_hdr_bleed_threshold" default="0.0">
The lower threshold of the HDR glow. When using the Mobile rendering method (which only supports a lower dynamic range up to [code]2.0[/code]), this may need to be below [code]1.0[/code] for glow to be visible. A value of [code]0.9[/code] works well in this case. This value also needs to be decreased below [code]1.0[/code] when using glow in 2D, as 2D rendering is performed in SDR.
</member>
<member name="glow_intensity" type="float" setter="set_glow_intensity" getter="get_glow_intensity" default="0.3">
The overall brightness multiplier of the glow effect. When using the Mobile rendering method (which only supports a lower dynamic range up to [code]2.0[/code]), this should be increased to [code]1.5[/code] to compensate.
</member>
<member name="glow_levels/1" type="float" setter="set_glow_level" getter="get_glow_level" default="1.0">
<member name="glow_levels/1" type="float" setter="set_glow_level" getter="get_glow_level" default="0.0">
The intensity of the 1st level of glow. This is the most "local" level (least blurry).
[b]Note:[/b] [member glow_levels/1] has no effect when using the Compatibility rendering method, due to this rendering method using a simpler glow implementation optimized for low-end devices.
</member>