maxColorAttachments property

How many colour attachments one render pass may open — gfx-50n.

One, or more. Asked rather than assumed, and the failure it guards against is the worst kind this interface has: on Impeller's OpenGL ES path a second attachment reaches an FML_CHECK, so the process aborts in release. It does not draw the wrong picture, log a warning or fall back — it stops. Every other capability here guards against something that produces a frame somebody can look at.

A number rather than a boolean for the reason maxAnisotropy is one: "does MRT work" and "how many" are different questions, and a deferred pass wanting four attachments has to be able to find out that it may have two.

What the engine does with a one: the scene pass stops declaring that it writes the surface buffer, so every node that reads it — occlusion, reflections, the shafts, the lens — is culled by the frame graph and reported as PassSkip.starved. Those effects are then off on that device and the frame is otherwise the frame it always was. A caller who wants to know why asks CompiledFrameGraph.skipped, which names the pass and the reason; nothing has to guess from a picture.

Opening more attachments than this throws rather than aborting, which is the promise that makes the number worth publishing.