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PORendering a line into a 1x1 RenderTarget2D does not change the target's pixel color
 

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  1. PORendering a line into a 1x1 RenderTarget2D does not change the target's pixel color
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    <p>What I am trying to achieve is the following: my pass will return a huge array with several unique numbers repeating over and over, which I need to retrieve and process on CPU.</p> <p>I tried rendering into a 2000x1 texture and then sampled it on the CPU with RenderTarget2d.GetData&lt;>() and a foreach loop. It was awfully slow :). So I sidestepped my problem, the idea now is to render to a 1x1 texture multiple times. Inbetween passes I will extend a parameter array in my shader to include the numbers already returned.Each pixel will than query the array and clip itself if it holds a number that already appeared.</p> <p>The problem now is that pixel color never changes nomatter what I render - it always returns some random numbers. When I added <code>Game.GraphicsDevice.Clear(Color.Transparent);</code> before the draw call it started returning zeroes, though the shader code should return 0.2f (or its 0 to 255 equivalent). Can it be because I render too small a content into it (I am drawing a line on the screen and sample the scene's color along the line) and it gets lerped at some point?</p> <p>C#/XNA code:</p> <pre><code> CollisionRT = new RenderTarget2D(Game.GraphicsDevice, 1, 1, false, SurfaceFormat.Color, DepthFormat.None); ... Game.GraphicsDevice.BlendState = BlendState.AlphaBlend; Game.GraphicsDevice.SetRenderTarget(CollisionRT); Game.GraphicsDevice.Clear(Color.Transparent); Game.GraphicsDevice.DepthStencilState = DepthStencilState.None; foreach (ModelMesh mesh in PPCBulletInvis.Model.Meshes) // PPCBulletInvis is a line that covers 1/18 of the screen (approx). { foreach (Effect effect in mesh.Effects) { //effect.Parameters["Texture"].SetValue(vfTex); effect.Parameters["halfPixel"].SetValue(halfPixel); effect.Parameters["sceneMap"].SetValue(sceneRT); effect.Parameters["World"].SetValue(testVWall.World); effect.Parameters["View"].SetValue(camera.View); effect.Parameters["Projection"].SetValue(camera.Projection); } mesh.Draw(); } Game.GraphicsDevice.SetRenderTarget(null); Rectangle sourceRectangle = new Rectangle(0, 0, 1, 1); Color[] retrievedColor = new Color[1]; CollisionRT.GetData&lt;Color&gt;(retrievedColor); Console.WriteLine(retrievedColor[0].R); // Returns zeroes. </code></pre> <p>Shader code:</p> <pre><code>float4x4 World; float4x4 View; float4x4 Projection; texture sceneMap; sampler sceneSampler = sampler_state { Texture = (sceneMap); AddressU = CLAMP; AddressV = CLAMP; MagFilter = POINT; MinFilter = POINT; Mipfilter = POINT; }; float2 halfPixel; struct VS_INPUT { float4 Position : POSITION0; }; struct VS_OUTPUT { float4 Position : POSITION0; float4 ScreenPosition : TEXCOORD2; }; VS_OUTPUT VertexShaderFunction(VS_INPUT input) { VS_OUTPUT output; float4 worldPosition = mul(input.Position, World); float4 viewPosition = mul(worldPosition, View); output.Position = mul(viewPosition, Projection); output.ScreenPosition = output.Position; return output; } float4 PixelShaderFunction(VS_OUTPUT input) : COLOR0 { input.ScreenPosition.xy /= input.ScreenPosition.w; float2 screenTexCoord = 0.5f * (float2(input.ScreenPosition.x,-input.ScreenPosition.y) + 1); screenTexCoord -=halfPixel; return (0.2f,0.2f,0.2f,0.2f);//tex2D(sceneSampler, screenTexCoord); } technique Technique1 { pass Pass1 { VertexShader = compile vs_3_0 VertexShaderFunction(); PixelShader = compile ps_3_0 PixelShaderFunction(); } } </code></pre>
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    1. UScubrman
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    1. COYou could try to render your line with XYZRHW to render to specific pixels. This should avoid the case that your geometry is clipped. Did you adjusted your viewport?
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      1. PORendering a line into a 1x1 RenderTarget2D does not change the target's pixel color
      1. USGnietschow
    2. COCould you please expand upon that, I can't clearly understand you at two points: what is XYZRHW? What I did try to avoid clipping was to write output.Position = (0,0,0,0); and output.Position = (1,1,1,1); in the VERTEX shader but it did not help - the pixel still holds 0,0,0,0. Secondly please tell me what you mean by "adjusting the viewport"?
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      1. PORendering a line into a 1x1 RenderTarget2D does not change the target's pixel color
      1. UScubrman
    3. COI think if you're rendering to a rendertarget with another dimension as the screen you have to adjust the size in the viewport of the graphicsdevice: http://msdn.microsoft.com/en-us/library/microsoft.xna.framework.graphics.viewport%28v=xnagamestudio.35%29.aspx. Could you try to set output.Position = (0,0,0,1)? XYZRHW is a type of vertexformat to set the position in screenspace not in worldspace, easier for screen-aligned rendering.
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      1. PORendering a line into a 1x1 RenderTarget2D does not change the target's pixel color
      1. USGnietschow
 

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