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OpenGL Particle Flicker in the distance

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I read the FAQ on Z-Fighting, but am unable to alter the Z-near / Z-far planes to adjust the issue (for good reasons). Also, 24-bit double-buffering appears to already be in use. I've landed in this mess of a project. For a brief description: There is map over which a plane flies. The map renders fine. There are also little 'Targets' on the map, which are drawn seperately from the map. They are small, and they move. At a distance they flicker, that is: in one frame they are drawn, in the next they are not (somewhat randomly). I must eliminate this flicker. The project will be used to run simulations of spotting those Targets, and flickering (of course) immediately draws the eye's attention, which would make any results from the simulations useless, since in real life things don't just disappear and reapper at random. I am fairly new to OpenGL, and am learning as much as possible, but I can't seem to find anything to help me out on this problem. Unfortunately we have no OpenGL expert around to help (Academic Research....). Anyone have any advice on eliminating, or at least drastically reducing the flicker that is occurring? Once the Targets get close enough to the camera the flicker effectively stops. As I already said, I've tweaked the Znear and Zfar planes as much as possible, but it's only helped some. Thanks for any help!

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Quote:
Original post by Glaiel_Gamer
i am new to openGL too, but try mipmapping
If the problem is z-fighting, which it certainly sounds like, mipmapping won't help. That only affects the texture quality. It is a good suggestion to use mipmapping with textures that will be seen from varying distances though, so if the map and targets are textured I would use mipmapping.

If you haven't read it yet, check out Learning to Love Your Z-buffer to get a better understanding of how the depth buffer works and how the near and far planes relate to it.

You may be able to get good results using glPolygonOffset. It needs to be enabled with one of the GL_POLYGON_OFFSET_* contants. See glEnable for more info on those. It is a pain to find good values for it however so I would avoid if it at all possible.

You shouldn't need to use polygon offset though if you have reasonable near and far plane values, so I'm curious why you can't adjust them anymore. Is it because the airplane and targets are too far apart? If that's the case you should be able to scale the world so that they are within a closer range so that you can use better values for the near and far planes.

EDIT: Another possible solution is to render with two separate frustums. The basic idea is you set the near and far planes so that they contain the farther away objects (the map and targets), render them, clear the depth buffer (important!), set the near and far plane values so that they contain the nearer objects (the airplane), then render that.

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Thanks for the suggestions. I don't think mipmapping will help any, since no textures are being applied to the Targets.

I'll read through the Z-buffer information you linked to; once I understand it better I may be able to tweak things more. I can't change the values now, since the plane is being shown from a chase perspective (so it's about 1 meter from the camera), flying at an altitude of 50-500 meters, and the camera is pointing at an angle of about 30 (Deg) from horizontal. So you see things out to the horizon.

I think the idea of rendering with two seperate frustrums sounds pretty promising, if I don't figure something better out from the readings.

Once again, thanks for the help. I'll try to remember to post a solution if I find one.

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Actually... Thinking about it a little more, I may be able to ignore the fact that we're in a chase view, since I won't need it for the purpose of my simulations (I'll just need to remember to change back the zNear value before someone else uses the code...)

I'll try some more tinkering...

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If that's your only reason for not changing the frustum then you should think about only changing the far clip plane and adding HW fog.

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I've moved the near clipping plane out; but it doesn't seem to affect the ficker at all.

Even when the Targets are just about to come inside the clipping plane (ie they are very close to it, but still in front of it) they still flicker. Maybe the problem is something different?

[edit]
So, umm.. I think the problem may actually just be that at the distance, the Targets only fill 1 or 2 pixels; so sometimes it decides that the pixel will be the Target color, and sometimes it decides the pixel will be the ground color. So there may not be a real solution to my flicker problem... maybe anti-aliasing on the Targets, so they get blurred over a couple of pixels?
[\edit]

[Edited by - Amitola85 on March 15, 2006 5:55:12 PM]

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Guest Anonymous Poster
I'm going to throw out the term 'Subpixel Accuracy'
because I think it may be relevant, Quake used to to avoid wierd jaggy skippy lines.
I have no idea how it works though, but hey, you never know...

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    • By DiligentDev
      This article uses material originally posted on Diligent Graphics web site.
      Introduction
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    • By LifeArtist
      Good Evening,
      I want to make a 2D game which involves displaying some debug information. Especially for collision, enemy sights and so on ...
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      LifeArtist
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      Hello. I am coding a small thingy in my spare time. All i want to achieve is to load a heightmap (as the lowest possible walking terrain), some static meshes (elements of the environment) and a dynamic character (meaning i can move, collide with heightmap/static meshes and hold a varying item in a hand ). Got a bunch of questions, or rather problems i can't find solution to myself. Nearly all are deal with graphics/gpu, not the coding part. My c++ is on high enough level.
      Let's go:
      Heightmap - i obviously want it to be textured, size is hardcoded to 256x256 squares. I can't have one huge texture stretched over entire terrain cause every pixel would be enormous. Thats why i decided to use 2 specified textures. First will be a tileset consisting of 16 square tiles (u v range from 0 to 0.25 for first tile and so on) and second a 256x256 buffer with 0-15 value representing index of the tile from tileset for every heigtmap square. Problem is, how do i blend the edges nicely and make some computationally cheap changes so its not obvious there are only 16 tiles? Is it possible to generate such terrain with some existing program?
      Collisions - i want to use bounding sphere and aabb. But should i store them for a model or entity instance? Meaning i have 20 same trees spawned using the same tree model, but every entity got its own transformation (position, scale etc). Storing collision component per instance grats faster access + is precalculated and transformed (takes additional memory, but who cares?), so i stick with this, right? What should i do if object is dynamically rotated? The aabb is no longer aligned and calculating per vertex min/max everytime object rotates/scales is pretty expensive, right?
      Drawing aabb - problem similar to above (storing aabb data per instance or model). This time in my opinion per model is enough since every instance also does not have own vertex buffer but uses the shared one (so 20 trees share reference to one tree model). So rendering aabb is about taking the model's aabb, transforming with instance matrix and voila. What about aabb vertex buffer (this is more of a cosmetic question, just curious, bumped onto it in time of writing this). Is it better to make it as 8 points and index buffer (12 lines), or only 2 vertices with min/max x/y/z and having the shaders dynamically generate 6 other vertices and draw the box? Or maybe there should be just ONE 1x1x1 cube box template moved/scaled per entity?
      What if one model got a diffuse texture and a normal map, and other has only diffuse? Should i pass some bool flag to shader with that info, or just assume that my game supports only diffuse maps without fancy stuff?
      There were several more but i forgot/solved them at time of writing
      Thanks in advance
    • By RenanRR
      Hi All,
      I'm reading the tutorials from learnOpengl site (nice site) and I'm having a question on the camera (https://learnopengl.com/Getting-started/Camera).
      I always saw the camera being manipulated with the lookat, but in tutorial I saw the camera being changed through the MVP arrays, which do not seem to be camera, but rather the scene that changes:
      Vertex Shader:
      #version 330 core layout (location = 0) in vec3 aPos; layout (location = 1) in vec2 aTexCoord; out vec2 TexCoord; uniform mat4 model; uniform mat4 view; uniform mat4 projection; void main() { gl_Position = projection * view * model * vec4(aPos, 1.0f); TexCoord = vec2(aTexCoord.x, aTexCoord.y); } then, the matrix manipulated:
      ..... glm::mat4 projection = glm::perspective(glm::radians(fov), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); ourShader.setMat4("projection", projection); .... glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp); ourShader.setMat4("view", view); .... model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f)); ourShader.setMat4("model", model);  
      So, some doubts:
      - Why use it like that?
      - Is it okay to manipulate the camera that way?
      -in this way, are not the vertex's positions that changes instead of the camera?
      - I need to pass MVP to all shaders of object in my scenes ?
       
      What it seems, is that the camera stands still and the scenery that changes...
      it's right?
       
       
      Thank you
       
    • By dpadam450
      Sampling a floating point texture where the alpha channel holds 4-bytes of packed data into the float. I don't know how to cast the raw memory to treat it as an integer so I can perform bit-shifting operations.

      int rgbValue = int(textureSample.w);//4 bytes of data packed as color
      // algorithm might not be correct and endianness might need switching.
      vec3 extractedData = vec3(  rgbValue & 0xFF000000,  (rgbValue << 8) & 0xFF000000, (rgbValue << 16) & 0xFF000000);
      extractedData /= 255.0f;
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