Rick Brewster

Anyway all this wasn't a total loss. I ported all of PDN's shaders over to ComputeSharp, which is a big win, and I learned a lot about pixel shaders and D2D's effects system. Some great stuff is coming in 4.4! (psst ... plugins will finally be able to use D2D and GPU rendering!)

Why isn't any of this part of D2D docs?! Nobody knows. Unfortunately, Direct2D is "complete" and Microsoft, IIUC, doesn't have many resources assigned to it, not even for fixing its terrible documentation.

And when it doesn't work at all you just get "intermediate texture too large" error codes. No debug output saying where or why or how or what. Nope. You have to guess, check, experiment. After a full week of this I'm throwing in the towel on a general-purpose SampleMap shader.

Direct2D's effect system also suffers from poor and inaccurate documentation, and insufficient descriptions of the algorithms that are employed behind the scenes. It's a FULLY opaque system... you can't even query the transform graph!

D2D limits intermediate textures in its effect rendering engine to 4K x 4K, which hurts, but raising that wouldn't matter -- max texture size on modern GPUs is 16K x 16K, so this limit would get hit anyway. One shader can't access more than that at once.

Or at least, you can't compute ahead-of-time which regions of the source input you'd need, unless you can run the shader first. You can do this if you're rendering "manually" with drawing calls, but you can't do it solely via the very "retained mode" effects system.

So, unfortunately, this particular experiment is a bust. I was really hoping to provide this for plugins to use! The key problem here is that for every output region (in fact, any output pixel), you potentially need access to the entire input image.

I've spent the last week trying every idea I can think of to tame the transform graph to try and minimize dependencies between nodes, or to cache vs not cache nodes at certain stages ... nope. No matter what I do, D2D just can't do it without gobbling up insane amounts of RAM.

(and that's only counting physical memory -- yeah, it'll commit gobs more, spilling out into the pagefile and filling your whole house with texture allocations)

Now for the bad news: Direct2D's effect system is REALLY REALLY REALLY bad when it comes to memory usage and I have not found a way to tame it. Running the SampleMap + PolarInversion shaders can consume all 24GB of my GeForce 3090's memory on an image that's only 16K x 16K pixels

I'd love to share all these gorgeous screenshots I'm taking, but I really don't want to ruin the surprises for anyone who has yet to reach those points, or play at all. It's worth going in as blind as you can.

I hit F12 to take a screenshot and it (Steam) must've processed the screenshot command either during or immediately after the hang

Game is Elden Ring, btw. It might be hard to parse the screenshot, but I'm rolling to the left to avoid a strike, just in the nick of time. NPC name and health bar is pixelated to avoid potential spoilers for folks.