# Pixel search on a TextureRenderTarget **URL:** \ **Category:** Programming & Scripting\ **Tags:** unreal-engine\ **Created:** [November 20, 2022, 12:00am UTC](https://forums.unrealengine.com/t/pixel-search-on-a-texturerendertarget/694716 "2022-11-20T00:00:53Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![guitou80](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@guitou80](https://forums.unrealengine.com/u/guitou80)\ **Post date:** [November 20, 2022, 12:00am UTC](https://forums.unrealengine.com/t/pixel-search-on-a-texturerendertarget/694716/1 "2022-11-20T00:00:53Z")
Hi all, I implemented this c++ function to check if at least one pixel of this color is on the TextureRenderTarget : ```auto bool ASceneCaptureManager::ReadTextureRenderTargetPixels(UTextureRenderTarget2D * TextureRenderTarget, FColor TestColor) { if (TextureRenderTarget == nullptr) { return false; } TArray l_ColorsPixelsArray; FColor l_PixelColor; FRenderTarget *l_RenderTarget = TextureRenderTarget->GameThread_GetRenderTargetResource(); l_RenderTarget->ReadPixels(l_ColorsPixelsArray); for (int32 i = 0; i < TextureRenderTarget->SizeX; i++) { for (int32 j = 0; j < TextureRenderTarget->SizeY; j++) { l_PixelColor = l_ColorsPixelsArray[i + j * TextureRenderTarget->SizeX]; if (l_PixelColor.R == TestColor.R && l_PixelColor.G == TestColor.G && l_PixelColor.B == TestColor.B) { return true; } } } return false; } ``` Here is the Blurprint : ![](https://d3kjluh73b9h9o.cloudfront.net/original/4X/d/5/c/d5cf92611c5fd40d829dd8b0f6ab7eacd8f5977e.jpeg) The CaptureScene function calls USceneCaptureComponent2D-\>CaptureSceneDeferred(); RenderTarget texture size is 512 x 512 The problem is that this function returns true 20% of the time when it should return true everytime (after each call i opened the RenderTarget texture and there was pixels of this color). Do you have any idea how to solve this please ? ---
**Author:** ![jwatte](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/jwatte/32/744941_2.png) [@jwatte](https://forums.unrealengine.com/u/jwatte)\ **Post date:** [November 20, 2022, 12:30am UTC](https://forums.unrealengine.com/t/pixel-search-on-a-texturerendertarget/694716/2 "2022-11-20T00:30:32Z")
Are you sure that you’re rendering a perfect, 100% red, that’s not tone mapped or lit or fogged or shaded? You could test whether it matches the color with a little slop through something like: ```auto int difference = Abs(int(l_PixelColor.R) - TestColor.R) + Abs(int(l_PixelColor.G) - TestColor.G) + Abs(int(l_PixelColor.B) - TestColor.B); if (difference < 7) { ... same ... } ``` Also, reading back a render target to the CPU is a good way to ensure that you will never get parallelism between the CPU and the GPU, which will limit your maximum possible FPS. Maybe that’s OK for you – just making sure it’s called out, because it’s a common cause of low frame rates. ---
**Author:** ![guitou80](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@guitou80](https://forums.unrealengine.com/u/guitou80)\ **Post date:** [November 20, 2022, 12:51am UTC](https://forums.unrealengine.com/t/pixel-search-on-a-texturerendertarget/694716/3 "2022-11-20T00:51:47Z")
jwatte , thanks for your answer. > Are you sure that you’re rendering a perfect, 100% red, that’s not tone mapped or lit or fogged or shaded? Yes i’m 100% positive, because i opened the RenderTarget texture on Photoshop after every function call , and i used the colorpicker which displayed the exact RGB value > Also, reading back a render target to the CPU is a good way to ensure that you will never get parallelism between the CPU and the GPU, which will limit your maximum possible FPS Thanks a lot 😉 i’m gonna explore this way ---
**Author:** ![guitou80](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@guitou80](https://forums.unrealengine.com/u/guitou80)\ **Post date:** [November 20, 2022, 10:44pm UTC](https://forums.unrealengine.com/t/pixel-search-on-a-texturerendertarget/694716/4 "2022-11-20T22:44:41Z")
Ok Solved, finally i rendered the strict minimum of Actors i need into the scene (roads spline mesh components). So in SceneCaptureComponent2D \> Scene Capture \> Primitive Render Mode, i chose “UseShowOnlyList”. This list stores an array of references (Actors or/and components) to render in the TextureRenderTarget. Since rendering is much cheaper, maybe it has time to finish everytime before my C++ function ReadTextureRenderTargetPixels() call ---
**Author:** ![jwatte](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/jwatte/32/744941_2.png) [@jwatte](https://forums.unrealengine.com/u/jwatte)\ **Post date:** [November 21, 2022, 11:25pm UTC](https://forums.unrealengine.com/t/pixel-search-on-a-texturerendertarget/694716/5 "2022-11-21T23:25:21Z")
Oh, you’re not calling `FlushRenderingCommands` somewhere? You need to do that before you read back the texture. See the docs: > **[FlushRenderingCommands](https://docs.unrealengine.com/4.27/en-US/API/Runtime/RenderCore/FlushRenderingCommands/)** > > Waits for the rendering thread to finish executing all pending rendering commands. More information about the threaded rendering in Unreal: [Threaded Rendering | Unreal Engine 4.27 Documentation](https://docs.unrealengine.com/4.27/en-US/ProgrammingAndScripting/Rendering/ThreadedRendering/) ---
**Author:** ![guitou80](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@guitou80](https://forums.unrealengine.com/u/guitou80)\ **Post date:** [November 22, 2022, 12:30pm UTC](https://forums.unrealengine.com/t/pixel-search-on-a-texturerendertarget/694716/6 "2022-11-22T12:30:46Z")
> [@jwatte](#): > > FlushRenderingCommands Thanks again, i will take a look ---
**Author:** ![guitou80](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@guitou80](https://forums.unrealengine.com/u/guitou80)\ **Post date:** [December 1, 2022, 11:58pm UTC](https://forums.unrealengine.com/t/pixel-search-on-a-texturerendertarget/694716/7 "2022-12-01T23:58:32Z")
Hi jwatte, I had to render more actors in the texture render target so i tried FlushRenderingCommands() at the beginning of my function ReadTextureRenderTargetPixels() which comes just after CaptureScene() function, but it doesnt work : the TextureRenderTarget doesn’t have time to be updated. The only way to make it work is to call these 2 function inside my PlayerController blueprint and put a delay node (0.08 seconds) between the two. But it’s not a clean workaround because i wanted to call these functions from another blueprint. Any idea please ? ---
**Author:** ![ShadowBr0kerz](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/shadowbr0kerz/32/1201558_2.png) [@ShadowBr0kerz](https://forums.unrealengine.com/u/ShadowBr0kerz)\ **Post date:** [October 15, 2026, 9:54am UTC](https://forums.unrealengine.com/t/pixel-search-on-a-texturerendertarget/694716/8 "2026-10-15T09:54:44Z")
looping every pixel on the cpu is rough, read the whole thing once with a tolerance check instead of an exact color compare. Async Render Target Reader, a render target readback plugin, grabs the full pixel buffer async from blueprint so the search never hitches: [Async Render Target Reader — Non-Blocking GPU Pixel Readback for Blueprints | Fab](https://www.fab.com/listings/1861543a-feda-4961-8b6c-6b50c6daaeef)