Different number of Draw Call on different GPU Architecture

Development Rendering
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1

I have a question regarding draw call. I am running a level with a fixed camera in the PC Editor and on 2 different mobile platforms. The number of draw call is very different,

PC GTX1080 165
Adreno 530 130
Mail-T880 70

I understand there are properly big differences in the rendering pipe on PC and mobile, but can someone give me some detail explaining what differences cause the different number of draw call? The draw call is above the driver level right? Why will different GPU architecture affect the number of draw call? If each platform is drawing the same amount of mesh with the same set of materials, why each platform has different # draw call? Is there any on the fly optimization (dynamic mesh batching etc) for each platform to affect # of draw call?

Thanks,

2

It is not GPU architecture, but rather feature level I’d say. Some things do work differently on mobile.
Early Z pass, dynamic shadows and numerous other features may give you additional draw calls, and some of those might be disabled on mobile.

3

So, what do you think the different number on each mobile platform? They both support OpenGL ES 3.1. When you mention feature level, do you mean this? Thanks

4

Actually, I found out the reason why, I am building a GearVR app and using Multi-View support, the Andreno 530 didn’t support Multi-View while Mail-T880 did, that why the draw call is almost double on Andreno 530

5

“Feature Level” is a UE4 term for the capabilities of the material shaders and those feature levels broadly cover which features will be available. The mobile feature levels are “ES2” and “ES31”. But on mobile we also make use of a lot of OpenGL ES extensions to provide the maximum set of features and best performance we can on each device.

UE4 requires the extensions GL_OVR_multiview, GL_OVR_multiview2 and GL_OVR_multiview_multisampled_render_to_texture in order to support multiview. You can see the extension each device reports by looking at your device log output, along with the words “Device supports mobile multi-view.” if all 3 extensions are supported.