# b_thangvn

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1. ## Precomputed atmospheric scattering...

Quote:Original post by ZealGamedev Yeah I am aware of that paper. Although you said Halo used a 'improved' version? Can you elaborate? In the meantime I have been playing around with the method venzon linked, and I am having trouble getting good results around dusk/dawn. Midday looks fine, but dusk/dawn with that method just doesnt come close to more advanced techniques like Erics... So have you tried to implement Eric's method ? I remember reading a paper about lighting effect on Halo 3 where they talked about their way of pre-computed atmospheric scattering. Maybe you can do a quick search on that.
2. ## Precomputed atmospheric scattering...

Try to look at Eric Bruneton's precomputed atmospheric scattering. It's great and you can extend on it. I believe Halo 3 and Reach use an improve version of his method.
3. ## Spark movement in car crash?

Hi OldProgie2, That's formula is great, I'm getting some result on my spark. I have some more questions if you don't mind: - So spread should be a vector with some default value, or should it be some random vector? - I still have trouble with world space. How do you keep the spark visible when the car moves really fast? P.S. Sorry, I need to clarify about the formula: so in the instance of the vehicle gliding against the wall, is it: V1 - Velocity of the wall V2 - Velocity of the vehicle ? Thanks. [Edited by - b_thangvn on July 2, 2010 8:37:39 PM]
4. ## Spark movement in car crash?

Hi unbird, Thanks for your input. I'll try out something like you suggested. In the mean time, I have this question: should I model the spark in world space or in model space? I can see each has advantages and disadvantages: - World space: I have hard time keeping the rotation and position of the spark to be in view when the car moves fast. However, I think world space will allow more realistic simulation. - Model space: great for keeping the spark visible with the car, but feel weird in some situations and not realistic. Thanks for your help.
5. ## Spark movement in car crash?

Hi Noxis, I do be able to get the normal at the collision point, but having trouble to use it to get the right emitting angle. I'm afraid I can't make a video since the game isn't my properties :(. Do you know any good way to do this, or maybe you know some good source that provide this info ? Thanks.
6. ## Spark movement in car crash?

Hi OldProgie2, Thanks for your input. I do transform my particle position into screen space and perform the scaling calculation. However, doing these give me a problem with car crash at high speed versus low speed. I want spark to be short on low speed impact, and long streak on high speed impact. Right now I don't really have a good way to do this. Also for the movement: I model gravity and dragging correctly, but having trouble with emitting angle. Right now I just emit the particle backward at high speed and straight up at slow speed, but it doesn't look great. Here is a pic of what I'm at: Thanks for your help.
7. ## Spark movement in car crash?

Hi Bangladesh, For the stretching, yes, new pos - old pos. Can you elaborate on the the car movement + camera movement? I'm working on the emitting angle but haven't found a good way for all the situations.
8. ## Spark movement in car crash?

Hi all, I've been trying to write a spark system for car crash. Something I would love to achieve is similar to this video: http://www.youtube.com/watch?v=YuAxXY9o4aI I have the particle system ready but I can't get the movement of the spark to work. I notice some time the spark moves forward, some time it moves backward, then other time it just flies everywhere. Also, how do you get the streak effect for the spark? I have a dot texture and I stretch it out but I'm not sure that's the best solution. All inputs are greatly appreciated. Thanks. [Edited by - b_thangvn on June 30, 2010 8:22:57 PM]
9. ## Spark for car crash?

Hi all, I've been trying to write a spark system for car crash. Something I would love to achieve is similar to this video: http://www.youtube.com/watch?v=YuAxXY9o4aI I have the particle system ready but I can't get the movement of the spark to work. I notice some time the spark moves forward, some time it moves backward, then other time it just flies everywhere. Also, how do you get the streak effect for the spark? I have a dot texture and I stretch it out but I'm not sure that's the best solution. All inputs are greatly appreciated. Thanks.
10. ## Help with particle rotation!

Hi guys, I'm modifying an existing spark particle system, which only has Y movement for now. I managed to add in the motion in X and Y direction but I would like to ask about the particle rotation in Z. So I have this particle texture to represent the streak, something like this: | | | and my coordinate is: positive Y up, positive X to the right, and positive Z is into the screen. I have the particle follows gravity but couldn't find a good way to rotate the particle around the z axis. I tried to store an old position and current position of the particle, then calculate the directional vector of the particle. I then transform it to camera space and take the tangent of x / y component of the directional vector. The problem I observe is that when I move the camera around, the rotation of the particle starts rotate in the opposite direction until it flips. I wonder how do you guys deal with the rotation of the particle. If you guys can give me some advice I would greatly appreciate it. Thanks in advance.
11. ## Sun effects (blooming)

Take a look at this one: http://www.mathematik.uni-marburg.de/~menzel/index.php?seite=tutorials Hope it helps.
12. ## atmospheric scattering implementation issue

Hi there, There are many papers on atmospheric scattering. I suggest check the one in GPU gems series, also the paper from Eric Bruneton.
13. ## Shadow map with direct light ?

Hi guys, Thanks for helping. @ Hodgman: It's interesting when you bring up PSSM because I've been looking at the PSSM articles in GPU Gems 3 and also at several CSM in ShaderX series. I also look through the CSM demo from NVIDIA OpenGL SDK. However, all the splitting view frustum is kinda out of my understanding right now :(. I just want to have a shadow map first, then I will dive into the splitting frustum scheme. So with that said, all the articles doesn't show me how to construct a bounding volume. I would greatly appreciate if you can point me to some resources :) ? @ szecs: You didn't see it coming did you :D ? It's interesting because I just watch your youtube demo a few days ago, but I didn't know it's you at the time. Great job on that.
14. ## Shadow map with direct light ?

Hi guys, So I finally want to have shadow in my demo and decide to implement it using shadow map. However, I have trouble figuring out how to implement shadow map with direct light. The general process to my understanding is: 1) Render the scene from the light perspective -> shadow map in a buffer 2) Perform rendering, and compare the depth of current pixel with value read out from shadow map to perform shadow shading. For spot light there are demos so I can understand step 1 because a spot light has a definitive world position, hence we can construct its world-view-projection matrix. But the direct light ( like the sun ), we won't have a position for it. We usually only have direction where the light comes from. So how do you render shadow map for direct light? Thanks in advance for all the help.
15. ## Atmospheric Scattering

Hi, Take a look at my implementation: http://www.youtube.com/watch?v=Q7DJq9Ph9js It's written using dx9 and hlsl. If you use dx10 it's even easier. Bruneton's demo is great cause it provides you with all the source. So sorry for the miss spelling. Anyway, if you decide to choose Bruneton approach, I can help you out with it. I don't know much about the other implementation, but I'm sure many ppl here have done it. P.S: Does anyone know how to embed youtube video straight in the post? Thanks.