I'm learning how to draw skybox using cubemaps from the following resource.
I've got to the part where he talks about how we can optimize the rendering of the skybox. I get that instead of rendering the skybox first, which will result in width*height of your viewport fragments to be calculated and then only to be overdrawn by other objects, it's best to draw it last and fake its depth value to be 1.0f by assigning the gl_Position of the skybox vertex shader to gl_Position = pos.xyww essentially making each gl_FragCoord.z equals to 1.0f due to perspective division.
Now after we get a skybox with each of its fragments have maximum depth value of 1.0f he changes the depth function to GL_LEQUAL instead of GL_LESS.
Here's where I got a little bit confused.
If we render the skybox last and have its depth values equal to 1.0f why do we need to change the depth function to GL_LEQUAL? Wouldn't it be sufficient to have it set to GL_LESS because if we render every other object in the scene it depth value will probably be less than 1.0f so it'll write its value to the z-buffer a value less than 1.0f. Now if we set the depth function for the skybox to GL_LESS it will then only pass the fragments with depth value of less than what is actually in the z-buffer which will probably only pass fragments that other objects are not covering, so why do we need the GL_LEQUAL?
When you initially cleared the framebuffer at the start of the frame, you probably did so to a value of 1.0f. So if you want to draw the skybox at all, you'll need to allow the skybox to draw in areas with a cleared depth value.
Related
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.
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.
If I use orthographic projection in OpenGL, but still set different z-values to my objects, does it still be visible in Depth Buffer?
I mean, in color buffer everything looks plain and at one distance. But wherever they will "colorized" in different shades? Does depth buffer "understand" depth in orthographic projection?
A depth buffer has nothing to do with the projection matrix. Simply put, a z-buffer takes note of the closest Z-value at a given point. As things are drawn it looks at the current value. If the new value is less then the existing value it is accepted and the z buffer is updated. If the value is greater then the value, behind the current value, it is discarded. The depth buffer has nothing to do with color. I think you might be confusing blending with depth testing.
For example, say you have two quads A & B.
A.z = - 1.0f;
B.z = - 2.0f;
If you assume that both quads have the same dimensions, outside of their Z value, then you can see how drawing both would be a waste. Since quad A is in front of quad B it is a waste to draw quad B. What the depth buffer does is checks the zcords. In this example if you had enabled depth testing & a depth buffer quad B would never have been drawn because the depth testing would have shown it was occluded by quad A.
I had an idea for fog that I would like to implement in OpenGl: After the scene is rendered, a quad is rendered over the entire viewport. In the fragment shader, this quad samples the depth buffer at that location and changes its color/alpha in order to make that pixel as foggy as needs be.
Now I know I can render the scene with the depth buffer linked to a texture, render the scene normally and then render the fog, passing it that texture, but this is one rendering too many. I wish to be able to either
Directly access the current depth buffer from the fragment shader
Be able to render the scene once, both to the normal depth buffer/screen and to the texture for fog.
Is this possible?
What you're thinking of (accessing the target framebuffer for input) would result in a feedback loop which is forbidden.
(…), but this is one rendering too many.
Why do you think that? You don't have to render the whole scene a new, just the fog overlay on top of it.
I wish to be able to either
Directly access the current depth buffer from the fragment shader
If you want to access only the depth of the newly rendered fragment, just use gl_FragCoord.z, this variable (that should only be read to keep performance) holds the depth buffer value the new fragment will have.
See the GLSL Specification:
The variable gl_FragCoord is available as an input variable from within fragment shaders
and it holds the window relative coordinates (x, y, z, 1/w) values for the fragment.
If multi-sampling, this value can be for any location within the pixel, or one of the
fragment samples. The use of centroid in does not further restrict this value to be
inside the current primitive. This value is the result of the fixed functionality that
interpolates primitives after vertex processing to generate fragments. The z component
is the depth value that would be used for the fragment’s depth if no shader contained
any writes to gl_FragDepth. This is useful for invariance if a shader conditionally
computes gl_FragDepth but otherwise wants the fixed functionality fragment depth.
Be able to render the scene once, both to the normal depth buffer/screen and to the texture for fog.
What's so wrong with first rendering the scene normally, with depth going into a separate depth texture attachment, then render the fog, finally compositing them. The computational complexity does not increase by this. Just because it's more steps, it's not doing more work that in your imagined solution, since the individual steps become simpler.
distance camera-pixel:
float z = gl_FragCoord.z / gl_FragCoord.w;
the solution you think to is a common solution, but no need of a supplementary sampling with a quad, everything is already there to compute fog in one pass if depth buffer is enable:
here is a an implementation
const float LOG2 = 1.442695;
float z = gl_FragCoord.z / gl_FragCoord.w;
float fogFactor = exp2( -gl_Fog.density *
gl_Fog.density *
z *
z *
LOG2 );
fogFactor = clamp(fogFactor, 0.0, 1.0);
gl_FragColor = mix(gl_Fog.color, finalColor, fogFactor );
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.