A function like “glReadPixels” in DirectX / SharpDX

问题

I'm searching for a way to read a pixels color at the mousepoint. In OpenGL it was done by calling the function "glReadPixels" after drawing the scene (or parts of it). I want to make a simple color picking routine in the background, for identifing a shapes / lines in 3D Space.

So, is there any equivalent method/function/suggestion for doing the same in SharpDX (DirectX10 / DirectX11) ?

回答1:

This is perfectly possible with Direct3D11: simply follow these steps:

Use DeviceContext.CopySubResourceRegion to copy part from the source texture to a staging texture (size of the pixel area you want to readback, same format, but with ResourceUsage.Staging)
Retrieve the pixel from this staging texture using Device.Map/UnMap.

There is plenty of discussion about this topic around the net (for example: "Reading one pixel from texture to CPU in DX11")

回答2:

Another option is to use a small compute shader, like :

Texture2D<float4> TextureInput: register(t0);
StructuredBuffer<float2> UVBuffer: register(t1);
RWStructuredBuffer<float4> RWColorBuffer : register(u0);

SamplerState Sampler : register( s0 );

[numthreads(1, 1, 1)]
void CSGetPixels( uint3 DTid : SV_DispatchThreadID )
{ 
float4 c = TextureInput.SampleLevel(Sampler , UVBuffer[DTid.x].xy, 0);
RWColorBuffer [DTid.x] = c;
}

It gives you the advantage of being a bit more "format agnostic".

Process is then like that.

Create a small structured buffer for UV (float2) (pixel position/texture size, don't forget to flip Y axis of course). Copy the pixel position you want to sample into this buffer.
Create a writeable buffer and a staging buffer (float4). Needs to be same element count as your uv buffer.
Bind all and Dispatch
Copy writeable buffer into the staging one.
Map and read float4 data in cpu

Please note I omitted thread group optimization/checks in compute shader for simplicity.

回答3:

Since you're using C#, my suggestion would be to use GDI+, as there is no such function like "glReadPixels" in DX. GDI+ offers very easy methods of reading the color of a pixel at your mouse pointer. Refer to stackoverflow.com/questions/1483928.

If GDI+ is a no go, as it isn't very fast, can't you stick to the usual object picking using a "Ray"? You want to identify (I suppose 3-dimensional) shapes/lines, this would be easy using a ray (and check for intersection) to pick them.

来源：https://stackoverflow.com/questions/13343020/a-function-like-glreadpixels-in-directx-sharpdx

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opengl

directx

sharpdx