Edit: Rendering the skybox before all other objects in the scene fixed this problem.
I've seen the question here but adding
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
doesn't appear to help.
I'm trying to render a spherical Skybox for my scene and for some reason when I Disable depth testing before doing so, the Skybox is the only thing rendered.
[Render other objects..]
// Disable depth test & mask, faceculling
glDisable(GL_DEPTH_TEST); // Adding this makes everything else invisible
glDepthMask(GL_FALSE);
glCullFace(GL_FRONT);
[Render texture onto inside of sphere..]
// Re-enable faceculling, & depth
glDepthMask(GL_TRUE);
glEnable(GL_DEPTH_TEST);
glCullFace(GL_BACK);
Any idea why this might be happening?
I wasn't sure of what code to include to keep this clear, so don't hesitate to ask for more.
Just to let you know, this:
glDisable(GL_DEPTH_TEST);
Disables both depth test and writing, so you don't need both that and set the depth mask to GL_FALSE.
When you clear the depth buffer each frame by default it should clear it the maximum value, probably 1.0. By default the depth function is GL_LESS meaning any depth value coming out of the fragment shader less than the one in the depth buffer passes and is written to the framebuffer.
It seems to me that what you're doing is clearing the depth buffer to 1.0, disabling depth testing and writing, drawing your objects, then enabling depth testing and writing and drawing your skybox. The problem with this is that the drawing of your objects doesn't write anything to the depth buffer, and so when it comes time to draw your skybox (with depth testing enabled) all the pixel depth values in the buffer are 1.0 (because you never wrote anything to it), and because the depth function is GL_LESS every pixel you draw of your skybox passes the depth test and is written to the framebuffer.
If there is a special need to have your objects always drawn in front of the skybox, for example the skybox follows the camera position around, then:
1) Disable the depth writing.
2) Draw the skybox.
3) Enable the depth writing.
4) Draw your objects.
Well, yes. That's what the depth test is for. Without it, there's nothing to indicate to OpenGL that the skybox shouldn't be rendered on top of everything else.
If you don't want this to happen, don't disable the depth test… or draw the skybox before everything else, instead of afterwards.
Related
I am trying to figure out how to render a skybox in a deferred renderer so that it can be included in post processing effects, However my Geometry stage is in view space and unfortunately the skybox in this stage will be effected by it's position relative to the light as any object would (it behaves like large box located very far from the light source and shows up very dark).
my setup without trying to incorporate the skybox in post processing is as follows:
1:(bind FBO) Render Geometry to color, normal, position FBO texture attachments (unbind FBO).
2:(bind FBO) Render the scene and calculate lighting in screen space.(unbind FBO)
3:(bind FBO) apply post processing effects (unbind FBO)
4: blit the Geometry FBO's depth buffer to the default frame buffer
5: render skybox.
I've tried to switch step 5 with 3
like this:
2:(bind FBO) Render the scene and calculate lighting in screen space.
5: render skybox
(unbind FBO)
3:(bind FBO) apply post processing effects (unbind FBO)
4: blit the Geometry FBO's depth buffer to the default frame buffer
but obviously the skybox has no depth information about the scene and renders on top of the lighting stage. And if I try to do any depth blitting between 2 and 5, I believe I am making invalid GL calls because I'm already bound to an FBO while calling
GL30.glBindFramebuffer(GL30.GL_READ_FRAMEBUFFER, DeferredFBO.fbo_handle);
GL30.glBindFramebuffer(GL30.GL_DRAW_FRAMEBUFFER, 0); // Write to default
// framebuffer or a skybox framebuffer
GL30.glBlitFramebuffer(0, 0, DisplayManager.Width,
DisplayManager.Height, 0, 0, DisplayManager.Width,
DisplayManager.Height, GL11.GL_DEPTH_BUFFER_BIT,
GL11.GL_NEAREST);
So I came up with a really easy hacky solution to this problem without having to incorporate any texture barriers or messing with the depth or color buffers.
I actually render the Skybox Geometry in the Geometry pass of the Deferred Rendering process, I render the skybox and set a flag in the fragment shader to color my skybox, remembering to modify the view matrix to remove the translation with another uniform flag in the vertex Shader. In the fragment shader I set the skybox color as such. Here is a basic summary without pasting all of the code.
layout (binding = 4) uniform samplerCube cubeMap;
uniform float SkyRender;
void main(){
if(SkyRender){
vec4 SkyColor = texture(cubeMap, skyTexCoords);
gAlbedoSpec.rgb = SkyColor.rgb;
gAlbedoSpec.a = -1;
}else{
gAlbedoSpec.rgb = texture(DiffuseTexture, TexCoords);
gAlbedoSpec.a = texture(SpecularTexture, TexCoords).r;
}
I set the alpha component of my skybox in the Color buffer as a flag for my Lighting pass. Here I set it to to -1.
In my lighting pass I simply choose to color my box with Diffuse Only instead of adding lighting calculations if my gAlbedoSpec alpha value is -1.
if(Diffuse.a > -1){
FragColor = SphereNormal * vec4(Dlighting, 1.0)+vec4(Slighting, 1.0);
}else{
FragColor = Diffuse ;
}
It's fairly simple and doesn't require much code and gets the job done.
Then give it the depth information it lacks.
When you rendered your scene in step 1, you used a depth buffer. So when you draw your skybox, you need an FBO that uses that same depth buffer. But this FBO also needs to use the color image that you rendered to in step 2.
Now, this FBO cannot be the same FBO you used in step 2. Why?
Because that would be undefined behavior. Presumably, step 2 reads from your depth buffer to reconstruct the position (if this is not the case, then you can just attach the depth buffer to the FBO from step 2. But then again, you're also wasting tons of performance). But that depth buffer is also attached to the FBO. And that makes it undefined behavior. Even if you're not writing to the depth, it is still undefined under OpenGL.
So you will need another FBO, which has the depth buffer from step 1 with the color buffer from step 2.
Unless you have access to OpenGL 4.5/ARB_texture_barrier/NV_texture_barrier. With that feature, it becomes defined behavior if you use write masks to turn off writes to the depth buffer. All you need to do is issue a glTextureBarrier before performing step 2. So you don't need another FBO if you have that.
In either case, keep the depth test enabled when rendering your skybox, but turn off depth writing. This will allow fragments behind your actual world to be culled, but the depth of the skybox fragments will be infinitely far away.
I'm trying to implement a deferred shader with OpenGL and GLSL and I'm having trouble with the light geometry. These are the steps I'm taking:
Bind multitarget framebuffer
Render color, position, normal and depth
Unbind framebuffer
Enable blend
Disable depth testing
Render every light
Enable depth testing
Disable blend
Render to screen
But since I'm only rendering the front face, when I'm inside a light it disappears completely, rendering the back face does not work, since I would get double the light power (And when inside, half [or the normal amount]).
How can I render the same light value from inside and outside the light geometry?
well in my case, i do it like that:
Bind gbuffer framebuffer
Render color, position, normal
Unbind framebuffer
Enable blend
Enable depth testing
glDepthMask(0);
glCullFace(GL_FRONT); //to render only backfaces
glDepthFunc(GL_GEQUAL); //to test if light fragment is "behind geometry", or it shouldn't affect it
Bind light framebuffer
Blit depth from gbuffer to light framebuffer //so you can depth-test light volumes against geometry
Render every light
If i remember correctly, in my deferred renderer i just render only the backfaces of the light volume. The drawback is you cannot depth test, you will only know if a light is behind a geometry after the light calculation is done and discard the pixel.
As another answer explained, you can do depth testing. Test for greater or equal to see if the backface is behind or on a geometry, therefore intersects with the surface of the geometry.
Alternatively you could check if you are inside the light volume when rendering and switch front faces accordingly.
I am drawing a cube and a line grid in 3D in OpenGL:
glBegin(GL_QUADS);
...
glEnd();
glBegin(GL_LINES);
...
glEnd();
Now, independent of the order (if I draw the lines first or the quads first) and independent of the position it always happens that the lines are draw over the cube. I thought OpenGL draws front to back.
What I tried is to use:
glEnable(GL_BLEND);
glBlendFunc (GL_ONE, GL_ONE);
which does work but part of the cube is transparent now.
I also tried glDepthFunc(GL_NEVER) with disabling glEnable (GL_DEPTH_TEST) but I get the same problem that the cube appears transparent.
Does anyone have a hint to overcome this problem?
If you want to draw the lines in the background, just draw them (and the rest of the background) first, clear the depth buffer, then render the rest of the scene.
Or you can just give the lines a depth such that they will always be behind everything else, but then you have to make sure that none of your gameworld objects go behind it.
Now, independent of the order (if I draw the lines first or the quads first) and independent of the position it always happens that the lines are draw over the cube.
IF your lines have proper depth, then you forgot to enable depth buffer. If you enabled depth buffer, then you must make sure that your library used for initializing OpenGL requested depth buffer.
I thought OpenGL draws front to back.
It does not. OpenGL draws polygons in the same order you specify them. There is no automatic sorting of any kind.
Does anyone have a hint to overcome this problem?
Well, you could clear depth buffer, but this will be slow and inefficient. Technically, you should almost never do that.
glDepthMask(GL_FALSE) will disable writing to depth buffer. i.e. any object drawn after that call will not update depth buffer but will use data that is already stored. It is frequently used for particle systems. So call glDepthMask(GL_FALSE), draw "lines", call glDepthMask(GL_TRUE), then draw cube.
If you combine glDepthMask(GL_FALSE) with glDepthFunc(GL_ALWAYS) then object will be always drawn, completely ignoring depth buffer (but depth buffer won't be changed).
I'm making a simple voxel engine (think Minecraft) and am currently at the stage of getting rid of occluded faces to gain some precious fps. I'm not very experimented in OpenGL and do not quite understand how the glColorMask magic works.
This is what I have:
// new and shiny
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// this one goes without saying
glEnable(GL_DEPTH_TEST);
// I want to see my code working, so fill the mask
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
// fill the z-buffer, or whatever
glDepthFunc(GL_LESS);
glColorMask(0,0,0,0);
glDepthMask(GL_TRUE);
// do a first draw pass
world_display();
// now only show lines, so I can see the occluded lines do not display
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
// I guess the error is somewhere here
glDepthFunc(GL_LEQUAL);
glColorMask(1,1,1,1);
glDepthMask(GL_FALSE);
// do a second draw pass for the real rendering
world_display();
This somewhat works, but once I change the camera position the world starts to fade away, I see less and less lines until nothing at all.
It sounds like you are not clearing your depth buffer.
You need to have depth writing enabled (via glDepthMask(GL_TRUE);) while you attempt to clear the depth buffer with glClear. You probably still have it disabled from the previous frame, causing all your clears to be no-ops in subsequenct frames. Just move your glDepthMask call before the glClear.
glColorMask and glDepthMask determine, which parts of the frame buffer are actually written to.
The idea of early Z culling is, to first render only the depth buffer part first -- the actual savings come from sorting the geometry near to far, so that the GPU can quickly discard occluded fragments. However while drawing the Z buffer you don't want to draw the color component: This allows you to switch of shaders, texturing, i.e. in short everything that's computationally intense.
A word of warning: Early Z only works with opaque geometry. Actually the whole depth buffer algorithm only works for opaque stuff. As soon as you're doing blending, you'll have to sort far to near and don't use depth buffering (search for "order independent transparency" for algorithms to overcome the associated problems).
S if you've got anything that's blended, remove it from the 'early Z' stage.
In the first pass you set
glDepthMask(1); // enable depth buffer writes
glColorMask(0,0,0); // disable color buffer writes
glDepthFunc(GL_LESS); // use normal depth oder testing
glEnable(GL_DEPTH_TEST); // and we want to perform depth tests
After the Z pass is done you change the settings a bit
glDepthMask(0); // don't write to the depth buffer
glColorMask(1,1,1); // now set the color component
glDepthFunc(GL_EQUAL); // only draw if the depth of the incoming fragment
// matches the depth already in the depth buffer
GL_LEQUAL does the job, too, but also lets fragments even closer than that in the depth buffer pass. But since no update of the depth buffer happens, anything between the origin and the stored depth will overwrite it, each time something is drawn there.
A slight change of the theme is using an 'early Z' populated depth buffer as a geometry buffer in multiple deferred shading passes afterwards.
To save further geometry, take a look into Occlusion Queries. With occlusion queries you ask the GPU how many, if any fragments pass all tests. This being a voxel engine you're probably using an octree or Kd tree. Drawing the spatial dividing faces (with glDepthMask(0), glColorMask(0,0,0)) of the tree's branches before traversing the branch tells you, if any geometry in that branch is visible at all. That combined with a near to far sorted traversal and a (coarse) frustum clipping on the tree will give you HUGE performance benefits.
z-pre pass can work with translucent objects. if they are translucent, do not render them in the prepass, then zsort and render.
I need to know how can I make the skybox appears as it's in the infinity??
I know that it's something related to depth, but I don't know the exact thing to disable or to enable??
First, turn off depth writes/testing (you don't need to bother with turning off depth testing if you draw the skybox first and clear your depth buffer):
glDisable(GL_DEPTH_TEST);
glDepthMask(false);
Then, move the camera to the origin and rotate it the inverse of the modelview matrix:
// assume we're working with the modelview
glPushMatrix();
// inverseModelView is a 4x4 matrix with no translation and a transposed
// upper 3x3 portion from the regular modelview
glLoadMatrix(&inverseModelView);
Now, draw your sky box and turn depth writes back on:
DrawSkybox();
glPopMatrix();
glDepthMask(true);
glEnable(GL_DEPTH_TEST);
You'll probably want to use glPush/PopAttrib() to ensure your other states get correctly set after you draw the skybox too (make sure to turn off things like lighting or blending if necessary).
You should do this before drawing anything so all color buffer writes happen on top of your sky box.
First, Clear the buffer.
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
Then, save your current modelview matrix and load the identity.
glPushMatrix();
glLoadIdentity();
Then render your skybox.
Skybox.render();
Then, clear the depth buffer and continue normally with rendering
glClear(GL_DEPTH_BUFFER_BIT);
OtherStuff.render();
glutSwapBuffers();
The only problem with drawing the sky box is first is that your pixel shader will execute for every pixel in the sky box. Just to be overwritten by other object in your world later on. Your best bet is to render all opaque object first then render your sky box. That way the pixel shader for the sky box only gets executed for the pixel who pass the z buffer test.
There is no infinity. A skybox is just a textured box, with normaly 0,0,0 in the middle.
Here is a short tut: link text
The best approach I can think of is to draw it on a first pass(or layer), then clear only the depth buffer. After that just draw the rest of the scene in another pass. This way the skybox will always remain "behind" the scene. Just remember to use the same camera for both passes and somehow snap the skybox to the camera.