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Asked: 2025-04-07T20:15:37+05:30

Why does the content of g_pSurfaceImg[0] get lost after accumulating previous frames in DirectX 10?

I’ve been diving into some DirectX 10 coding, and I’ve run into a frustrating issue that I can’t seem to resolve. I’m trying to create this sort of trailing effect where the previous frames accumulate on `g_pSurfaceImg[0]`. The idea is to shift the image to the right and let the previous states blend in, creating a smooth trailing effect. But the weirdest thing happens: the content of `g_pSurfaceImg[0]`, instead of accumulating and fading nicely, just… well, it disappears or gets lost somehow after the previous frames accumulate.

I’ve set up everything properly: I’ve created multiple render target views for my surfaces and applied different pixel shaders that should allow for blending with alpha. However, when drawing to `g_pSurfaceImg[0]`, it seems like it just wipes out whatever was previously there instead of blending it properly. Instead of seeing this smooth transition of trailing effects, it looks like the image is just shifting without the expected fade effect.

I’ve tried flicking through my shaders and render target states, but nothing seems to yield the desired results. One critical point I’ve spotted is during the resource setup. Am I using the correct blend states for the rendering operation? Maybe when I set up the render targets, I’m mishandling them, causing the old content to vanish. Plus, there’s this part where I’m creating a shader resource view on `g_pSurfaceImg[0]`—could that be where things are going awry?

I’m also checking if the multisampling setup might be an issue. It seems like the surface has been set up correctly, but despite following what the DirectX docs say, the output remains a mystery.

Have you encountered something similar? Where does the content go after the accumulation? Feel free to drop any suggestions or insights on how I might ensure that the content persists instead of just shifting over.

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    2 Answers

    1. Sounds like you’re having a tough time with that trailing effect! It can be pretty tricky to get blending right in DirectX, especially when you’re trying to accumulate frames. Here are a few things you might want to double-check:

      • Blend States: Make sure your blend state is set up correctly. You may need a blend state that allows for alpha blending. Something like this could work:
        • BlendStateDesc.BlendEnable[0] = TRUE;
BlendStateDesc.SrcBlend = D3D11_BLEND_SRC_ALPHA;
BlendStateDesc.DestBlend = D3D11_BLEND_INV_SRC_ALPHA;
BlendStateDesc.BlendOp = D3D11_BLEND_OP_ADD;
      • Render Target Views: Ensure that you’re binding your render targets correctly before drawing. If you don’t bind `g_pSurfaceImg[0]` properly before drawing, you might be writing to the wrong target.
      • Clear Flags: Check if you are clearing the render target every frame or if you are incorrectly using depth/stencil views. If you clear it, it will wipe out previous content!
      • Pixel Shader Logic: Look over your pixel shader. Make sure it correctly blends the current pixel with the previous pixel from `g_pSurfaceImg[0]` based on alpha values.
      • Resource Setup: When you create your shader resource view for `g_pSurfaceImg[0]`, make sure you’re not unintentionally overwriting the contents of the render target when binding it as a shader resource.

      Also, multisampling can mess things up if not set correctly. Ensure you have the correct sample count and quality. Sometimes trying with single sampling can help in debugging this issue.

      If you’ve looked through all these and it’s still acting weird, maybe try outputting the pixel values to a debug buffer after rendering to see what’s actually happening. That could give you some clues on where things are going wrong.

      Good luck! It’s all about trial and error. Keep tweaking those parameters and see if anything shifts the output in the right direction.

    2. From your description, it sounds like the issue stems directly from your current blend state configuration. When attempting to create a trail or accumulation effect in DirectX 10, make sure your current render target blend state is configured correctly: specifically, you’ll want to enable blending, typically using something like SrcAlpha for the source and InvSrcAlpha or One for the destination blend factors. If your blend mode is set to default (overwrite), the new render operation will simply replace existing content rather than accumulate it. Ensure that in your output merge stage you’re using something similar to this blend setup: BlendEnable = TRUE; SrcBlend = Src_Alpha; DestBlend = Inv_Src_Alpha; or alternately SrcBlend = One; DestBlend = One; if you want additive accumulation. Additionally, double-check your alpha values being output from your pixel shader—if your alpha is zero or improperly set, blending won’t behave as expected, causing previously drawn content to vanish visually.

      Another place to investigate closely is resource binding, specifically how and when you’re switching render target and shader resource views. Keep in mind that in Direct3D10, you cannot simultaneously bind a resource as both the render target (output) and shader resource (input). Accidentally binding the same resource simultaneously will result in undefined behavior, often causing cleared, blank, or corrupted content. To debug this, explicitly unbind your surfaces from shader resource slots before using them as render targets, and vice versa. Also verify no unintended clears are being called when switching render targets—your trail effect depends on persistent, incremental rendering, so any unintended clearing would naturally disrupt the trailing accumulation. Lastly, although your multisample setup may be correct, temporarily disable multisampling if you’re suspecting it’s complicating matters, as multisampling may sometimes complicate render target configuration and blending behavior.