• Advertisement
Sign in to follow this  

OpenGL Non-fullscreen Anti-Aliasing with OpenGL and SDL

This topic is 2406 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

I have been looking at various anti-aliasing options in OpenGL, and none of them seems to provide what i want.
The ARB_multisample extension -AFAIK- is only for /full screen/ anti-aliasing, where as the core opengl polygon antialiasing requires me to
sort my polygons in depth order.
Is there a way to combine the 2 ? i.e. a non fullscreen anti-aliasing technique that *just works* ?

Thanks in advance.

P.S : I use OpenGL w/ SDL

Share this post


Link to post
Share on other sites
Advertisement

Is there a way to combine the 2 ? i.e. a non fullscreen anti-aliasing technique that *just works* ?

Can you be more precise on what you mean by "non fullscreen anti-aliasing" ? Antialiasing only part of a window ? Only one viewport ? Only selected primitives ?

MSAA and the old style line/polygon smoothing are two totally independent techniques, each with their respective limitations. First off, you should probably rethink your approach. Why can't you just antialias everything and be done with it ? That would certainly be the most efficient way.

Now, it is possible to have parts of your scene rendered with antialising and parts without by using multiple FBOs with different multisampling settings. It's rather trivial if they affect distinct parts of the screen. It's harder if MSAA settings are to be mixed within the same render area. Except for a few special cases (eg. having a reflection rendered without AA, but the rest of the scene with AA) this approach is not usually advisable.

Share this post


Link to post
Share on other sites
I think when he says fullscreen he means not windowed mode? In other words the viewport covers the entire display (I could be wrong). I think multisample antialias should work in fullscreen as well as in windowed mode.. again, I could be wrong...

I have noticed that some nVidia chipsets have had some problems with msaa, it might require some driver tinkering to get working.

Share this post


Link to post
Share on other sites

I think when he says fullscreen he means not windowed mode?



Yeah, that's a common misunderstanding that "FS" in "FSAA" means "full-screen" (it's "full-scene"). There is no difference whether the window covers entire screen or not.

Share this post


Link to post
Share on other sites
Oh..k. Sorry for the confusion.
I assumed the FS in FSAA to mean Full-Screen since it didn't work for me in windowed mode. Well, it didn't work in full screen mode either...
Please tell me what i'm doing wrong :

i am using SDL w/ OpenGL on ubuntu10.10
i have an ati-radeon card w/ fglrx installed

After SDL_Init, i do :

SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 4);

and after SDL_SetVideoMode,

glEnable( GL_MULTISAMPLE );

But i don't see any multisampling going on.

What's worse is that if i run the same program on my intel laptop w/ inbuilt graphics card, the program /segfaults/ on the first gl call following SetVideoMode.
If i free the sdl_surface immediately after SetVideoMode and call SetVideoMode again, i don't see any segfault, but i don't see any AA either.

P.S : glGetString( GL_EXTENSIONS ); does print GL_ARB_multisample on both my laptops.

Please tell me what i'm missing.
Thank you.

Share this post


Link to post
Share on other sites



After SDL_Init, i do :

SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 4);

and after SDL_SetVideoMode,

glEnable( GL_MULTISAMPLE );

But i don't see any multisampling going on.


And what do SDL_GL_GetAttribute() for those attributes say after SDL_SetVideoMode? Or glGetInteger with GL_SAMPLE_BUFFERS_ARB/GL_SAMPES_ARB?
And also, are there any visuals supporting multisampling? Check output of glxinfo. In the table with visuals, look for "ms" column. "ns" there is number of samples, and "b" is number of buffers.


What's worse is that if i run the same program on my intel laptop w/ inbuilt graphics card, the program /segfaults/ on the first gl call following SetVideoMode.
If i free the sdl_surface immediately after SetVideoMode and call SetVideoMode again, i don't see any segfault, but i don't see any AA either.
[/quote]

What do you mean "I free sdl_surface"? You should not ever free the surface returned by SDL_SetVideoMode. If you need another video mode, just call SDL_SetVideoMode again.

Share this post


Link to post
Share on other sites
Capricorn,
On my intel laptop (no dedicated graphics card), i tried glxinfo. It showed me no visuals with non-zero ms and b. Does this mean i can't have multisampling on this laptop?, or is there something i can try to make it happen. And, yeah, SDL_GetAttribute returned 0, 0 too. Also, are all opengl games i run on this laptop doomed to look jaggy?
I'll try the same on my ati-radeon laptop when i get home.

Thanks!

Share this post


Link to post
Share on other sites
Short answer is yes, you can't have multisampling. Long answer is: check your video driver documentation for clues on enabling FSAA. nVidia drivers, for example, allow you to set __GL_FSAA_MODE environment variable prior to launching application, thus overriding any AA settings. Even then, if you don't have any ms-capable visuals, it's up to driver. Though I must tell I have little faith in both Intel's and ATI's Linux drivers anyway.

Share this post


Link to post
Share on other sites
Oh.. that's sad.
Btw, on ati-radeon laptop, i do see ms capable visuals. I tried using the buffer sizes mentioned in the glxinfo listing with multisampling,
but still i see no AA going on.
Also, SDL_GetAttribute returns 4 and 1 for samples and buffers respectively.

What's happening?

Thank you.

P.S : i am still not able to convince myself that there i have no anti-aliasing solution available.
Isn't there some some crude method to fall back to?, a software implementation perhaps? Something...

Share this post


Link to post
Share on other sites

Oh.. that's sad.
Btw, on ati-radeon laptop, i do see ms capable visuals. I tried using the buffer sizes mentioned in the glxinfo listing with multisampling,
but still i see no AA going on.
Also, SDL_GetAttribute returns 4 and 1 for samples and buffers respectively.
What's happening?



Are you sure? Take two identical screenshots with and without AA and compare them. If SDL reports MS buffers are present, it should work (with glEnable(GL_MULTISAMPLE)). Try drawing some simple lines, or a triangle with severly extruded angle, it's easier to compare this way.


P.S : i am still not able to convince myself that there i have no anti-aliasing solution available.
Isn't there some some crude method to fall back to?, a software implementation perhaps? Something...
[/quote]

Well, older techniques include antialiasing using accumulation buffer. The idea is to render a frame several times into accumulation buffer introducing some jitter for projection transformation (so that resulting frame is shifted by very small amounts in different directions). Google for that, there's plenty of info out there. But keep in mind that this method comes with significant overhead. It's for you to decide if the goal worth the hassle :)

Share this post


Link to post
Share on other sites

P.S : i am still not able to convince myself that there i have no anti-aliasing solution available.
Isn't there some some crude method to fall back to?, a software implementation perhaps? Something...

I'm afraid you won't get anywhere with an Intel graphics chipset:

Source: Intel

Intel chipsets with integrated graphics do not support full scene anti-aliasing. Anti-aliased lines are supported in OpenGL* applications.
[/quote]

Now, alternatives do exist. The traditional approaches include supersampling or accumulation (or FBO) based jittering methods that were already mentioned. None of these will realistically work on Intel GPUs, as they require vast amounts of memory and rendering performance. In fact MSAA (multisampling AA, the most common form of FSAA) was developed to counter the huge resource requirements of the two previously mentioned algorithms.

Recently, a number of new shader based post processing FSAA algorithms were developed. The basic idea is to detect edges and blur them during a post-process. Some AAA games use these techniques to some extend, including Crysis AFAIR. The intent is to minimize the memory consumption of typical MSAA and circumvent limitations of MSAA with respect to deferred buffers. However even though these algorithms require less memory than large kernel MSAA, they are still very shader intensive. It is rather unlikely that they will function properly on very low end chips such as Intel GPUs.

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Tags

  • Advertisement
  • Popular Now

  • Similar Content

    • By QQemka
      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;
    • By Devashish Khandelwal
      While writing a simple renderer using OpenGL, I faced an issue with the glGetUniformLocation function. For some reason, the location is coming to be -1.
      Anyone has any idea .. what should I do?
    • By Andrey OGL_D3D
      Hi all!
      I try to use the Sun shafts effects via post process in my 3DEngine, but i have some artefacts on final image(Please see attached images).
      The effect contains the following passes:
      1) Depth scene pass;
      2) "Shafts pass" Using DepthPass Texture + RGBA BackBuffer texture.
      3) Shafts pass texture +  RGBA BackBuffer texture.
      Shafts shader for 2 pass:
      // uniform sampler2D FullSampler; // RGBA Back Buffer uniform sampler2D DepthSampler; varying vec2 tex; #ifndef saturate float saturate(float val) {     return clamp(val, 0.0, 1.0); } #endif void main(void) {     vec2 uv = tex;     float sceneDepth = texture2D(DepthSampler, uv.xy).r;     vec4  scene        = texture2D(FullSampler, tex);     float fShaftsMask     = (1.0 - sceneDepth);     gl_FragColor = vec4( scene.xyz * saturate(sceneDepth), fShaftsMask ); } final shader:
      // uniform sampler2D FullSampler; // RGBA Back Buffer uniform sampler2D BlurSampler; // shafts sampler varying vec4 Sun_pos; const vec4    ShaftParams = vec4(0.1,2.0,0.1,2.0); varying vec2 Tex_UV; #ifndef saturate  float saturate(float val) {     return clamp(val, 0.0, 1.0); } #endif vec4 blendSoftLight(vec4 a, vec4 b) {   vec4 c = 2.0 * a * b + a * a * (1.0 - 2.0 * b);   vec4 d = sqrt(a) * (2.0 * b - 1.0) + 2.0 * a * (1.0 - b);       // TODO: To look in Crysis what it the shit???   //return ( b < 0.5 )? c : d;   return any(lessThan(b, vec4(0.5,0.5,0.5,0.5)))? c : d; } void main(void) {     vec4 sun_pos = Sun_pos;     vec2    sunPosProj = sun_pos.xy;     //float    sign = sun_pos.w;     float    sign = 1.0;     vec2    sunVec = sunPosProj.xy - (Tex_UV.xy - vec2(0.5, 0.5));     float    sunDist = saturate(sign) * saturate( 1.0 - saturate(length(sunVec) * ShaftParams.y ));     sunVec *= ShaftParams.x * sign;     vec4 accum;     vec2 tc = Tex_UV.xy;     tc += sunVec;     accum = texture2D(BlurSampler, tc);     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.875;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.75;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.625;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.5;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.375;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.25;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.125;     accum  *= 0.25 * vec4(sunDist, sunDist, sunDist, 1.0);           accum.w += 1.0 - saturate(saturate(sign * 0.1 + 0.9));     vec4    cScreen = texture2D(FullSampler, Tex_UV.xy);           vec4    cSunShafts = accum;     float fShaftsMask = saturate(1.00001 - cSunShafts.w) * ShaftParams.z * 2.0;              float fBlend = cSunShafts.w;     vec4 sunColor = vec4(0.9, 0.8, 0.6, 1.0);     accum =  cScreen + cSunShafts.xyzz * ShaftParams.w * sunColor * (1.0 - cScreen);     accum = blendSoftLight(accum, sunColor * fShaftsMask * 0.5 + 0.5);     gl_FragColor = accum; } Demo project:
      Demo Project
      Shaders for postprocess Shaders/SunShaft/
      What i do wrong ?
      Thanks!
       


  • Advertisement