For a game the conventional method of painting a set of semi transparent clouds and rigging them to a basic particle system is the normal convention but for a full blown animation there are more options to choose from. The best solution at the moment for creating effects such as dust, flames and fumes are by far volumetric particles since instead of using intersecting planes these primarily use voxels to fill an area with a semi-transparent 'fog'. Using the voxel method dynamic fluid effect can be simulated realistically with buoyancy and temperature etc.
FumeFX is one of the leading pieces of software that convert 3D objects onto volumetric sources and one of its ground breaking features is the possibility to simulate fluid effects including velocities. My particle effects where created using thinking particles so the fluid simulations where not necessary to my dynamics and the reason for me not using the physics from the FumeFX alone is because it cannot shape the voxels it can only simulate. For my simulation i had disabled most of the physics since they had been created using the particles themselves but i did use it to simulate and animate fuel, smoke and dissipation. Overall the combination of thinking particles to shape the explosion and then simulation them with FumeFX to convert them into volumetric voxels provides unparalleled control over the system. With the particle voxel combination the dust and explosions can be simulated but its Vray that really brings the cake to the table, Vray is able to understand volumetric particles and not only illuminate them but it scatters the light within the voxels themselves to calculate optical density including changes in colour.
Finally one system i had discovered simply by chance is that setting up a camera for the particle system alone allows me to separately render a z-depth pass on it allowing very easy post production tweaks. Withe the z-depth alpha maps, as the particles develop they can be reshaped re coloured or or even removed entirely.
Saturday, 10 December 2011
Thinking particles...
For the central explosion i began working with 3ds max's primitive Pflow particle generator, this is a basic particle generation system that provides particles with positions, velocities, alignments and other properties and is a good system for creating simple events such as an explosion but thats just about it. For my scene i had implemented a more complex 3rd party system called thinking particles, this system not only provides the basic particle functions but using a flow graph systems it creates groupes and events as well as providing complete feedback for each individual particle. This particle system integrates an entirely new piece of software into the existing 3ds max which is a new learning curve but with the understanding of thinking particles particles can be manipulated in almost every way possible.
For my explosion i had analysed mt references and broke it down onto separate pieces which would be rendered separately for the uppermost realism. The explosion begins with an intense flash of light as the explosives react and the blast wave shoots from the origin across the ground, the flash then bubbles outwards and creates a dense fog as the fire dies. As the explosion bubbles a secondary blast fires away from the ground high into the dragging along anything in its path shooting rocks and other debris into the air. The debris itself leaves a trail of smoke and finally the entire thing dissipates into the air. For my system i broke it down into 3 parts being the wave the bubble and the blast each where simulated and rendered separately since the bubbly flames produced a bright glow and a dense smoke unlike the wave which seem fluffy with a low opacity.
For the wave i generated particles along the surface in a circular motion by limiting their direction to a random XY spread and as they spread they create particles along their path in a circular motion. For the bubbling explosion i sent a small number of particles away from the center in a circular motion but these rise as if they had temperature buoyancy and from these particles where created in a spherical shape leaving some behind. Finally the blast shoots a small number of particles through the bubbles and puches some upwards, also leaving a trail from the primer. All of the particles generated using TP where finally influenced by a physics setup which included friction turbulence and gravity all made with a flow-graphing system.
For my explosion i had analysed mt references and broke it down onto separate pieces which would be rendered separately for the uppermost realism. The explosion begins with an intense flash of light as the explosives react and the blast wave shoots from the origin across the ground, the flash then bubbles outwards and creates a dense fog as the fire dies. As the explosion bubbles a secondary blast fires away from the ground high into the dragging along anything in its path shooting rocks and other debris into the air. The debris itself leaves a trail of smoke and finally the entire thing dissipates into the air. For my system i broke it down into 3 parts being the wave the bubble and the blast each where simulated and rendered separately since the bubbly flames produced a bright glow and a dense smoke unlike the wave which seem fluffy with a low opacity.
For the wave i generated particles along the surface in a circular motion by limiting their direction to a random XY spread and as they spread they create particles along their path in a circular motion. For the bubbling explosion i sent a small number of particles away from the center in a circular motion but these rise as if they had temperature buoyancy and from these particles where created in a spherical shape leaving some behind. Finally the blast shoots a small number of particles through the bubbles and puches some upwards, also leaving a trail from the primer. All of the particles generated using TP where finally influenced by a physics setup which included friction turbulence and gravity all made with a flow-graphing system.
VRay...
For the entire scene i have been using the newly released Vray 2.0, This renderer provides a realtime renderes that utilizes the full potential of my GPU. One of vrays key features appart from the realistic lighting solutions is the Vray physical camera, this is similar to any other virtual cam but has all of the settings of a real camera such as exposure time, vignetting and shutter angle weather it be for a still cam or a camcorder, analogue or digital.
When using a realistic renderer its easy to have render time of going into hours per frame especially when calculating global illumination for each frame and fine details so it is essential to have a good understanding of the renderer and general illumination settings.
For this project i had begin with a render time of 30minutes per fram and with each scene containing up to 1150 frames i would need about 1725 hours to render before post production, particle simulation and geometry caches. To reduce this time i had started with the illumination settings, this would reduce the lighting quality but preserve the overall look of the scene. Taking the z-depth into consideration most of the illumination wasn't necessary so for each shot I had analysed what was relevant to the final comp and began adapting.
The default Vray settings are modified to suit an indoor architectural scene but since my shots were all out doors i had altered the presets drastically. To start with the default settings combine an irradiance map with brute force GI and for my outdoor scene the addition of the brute force pass was completely unnecessary. Brute force GI calculations renders the scene using the Vray renderers core lighting algorithms and caches nothing, this solution is by far the most accurate when specified but at the highest price of render time and since my scene had no glass properties or extremely fine detail such as fur or hi-res HDRI's the brute orce approche was dismissed. For all of the scenes Vrays irradiance map was used, this approach creates a light map using rays from the camera and interpolates the illumination by blurring nearby samples so for an outdoor scene natural haze and dust a sharp crisp intior solution can be substituted for the irradiance map.
My settings for the first scene used and extremely low sampling rate of -3 / -4 since its a flat planar scene including have and dust but i had set the sub-sample divisions to a high value of 50 to separate the shadows of the grass. One problem with the irradiance map is that the samples are randomised (for best results) so for the finer details of a static objects, such at the grass, flickering can occur, to overcome this i rendered the map using the cameras entire path and localised the randomisation per sample so that in each frame each area would have the same rate of sub sampling. The second scene also uses a low sample rate but without any fine details the sub-sampling divisions was lowered to just 10 without a reduction in image quality. this was mainly due to the addition of motion blur with a look up rate of only 2 frames in either direction. The final shot included the main explosion, this explosion had an extremely low voxel value since it was made up of volumetric particles and these voxels both received and emitted vray GI as well as scattering them within the cloud so a high sampling rate was crucial to fully capture the lighting within the voxels. With a high rate of samples, 1 / 3 i had used a low sub-sample devision value of 10.
The scene is globally lit with the vray sky map which is linked to a vray sun node which illuminates the entire scene with even lighting but only produces 25000 photons which which are focused into a specific area. Using the light cache or the photon map GI solutions and caustics, refractive or reflective, could only be generated within the specified area as well as environmental effects such as fog or volumetric lighting. Thankfully though Vrays modified irradiance map works on real world intensity principles such as Lux and lumens so all GI effects can be rendered wherever the camera points. irradiance maps can also be generated without rendering or incrementally during rendering which save huge amounts of time hen rendering a static scene. For my scene however, with the volumetric effects the best results were from creating new light maps for each frame.
When using a realistic renderer its easy to have render time of going into hours per frame especially when calculating global illumination for each frame and fine details so it is essential to have a good understanding of the renderer and general illumination settings.
For this project i had begin with a render time of 30minutes per fram and with each scene containing up to 1150 frames i would need about 1725 hours to render before post production, particle simulation and geometry caches. To reduce this time i had started with the illumination settings, this would reduce the lighting quality but preserve the overall look of the scene. Taking the z-depth into consideration most of the illumination wasn't necessary so for each shot I had analysed what was relevant to the final comp and began adapting.
The default Vray settings are modified to suit an indoor architectural scene but since my shots were all out doors i had altered the presets drastically. To start with the default settings combine an irradiance map with brute force GI and for my outdoor scene the addition of the brute force pass was completely unnecessary. Brute force GI calculations renders the scene using the Vray renderers core lighting algorithms and caches nothing, this solution is by far the most accurate when specified but at the highest price of render time and since my scene had no glass properties or extremely fine detail such as fur or hi-res HDRI's the brute orce approche was dismissed. For all of the scenes Vrays irradiance map was used, this approach creates a light map using rays from the camera and interpolates the illumination by blurring nearby samples so for an outdoor scene natural haze and dust a sharp crisp intior solution can be substituted for the irradiance map.
My settings for the first scene used and extremely low sampling rate of -3 / -4 since its a flat planar scene including have and dust but i had set the sub-sample divisions to a high value of 50 to separate the shadows of the grass. One problem with the irradiance map is that the samples are randomised (for best results) so for the finer details of a static objects, such at the grass, flickering can occur, to overcome this i rendered the map using the cameras entire path and localised the randomisation per sample so that in each frame each area would have the same rate of sub sampling. The second scene also uses a low sample rate but without any fine details the sub-sampling divisions was lowered to just 10 without a reduction in image quality. this was mainly due to the addition of motion blur with a look up rate of only 2 frames in either direction. The final shot included the main explosion, this explosion had an extremely low voxel value since it was made up of volumetric particles and these voxels both received and emitted vray GI as well as scattering them within the cloud so a high sampling rate was crucial to fully capture the lighting within the voxels. With a high rate of samples, 1 / 3 i had used a low sub-sample devision value of 10.
The scene is globally lit with the vray sky map which is linked to a vray sun node which illuminates the entire scene with even lighting but only produces 25000 photons which which are focused into a specific area. Using the light cache or the photon map GI solutions and caustics, refractive or reflective, could only be generated within the specified area as well as environmental effects such as fog or volumetric lighting. Thankfully though Vrays modified irradiance map works on real world intensity principles such as Lux and lumens so all GI effects can be rendered wherever the camera points. irradiance maps can also be generated without rendering or incrementally during rendering which save huge amounts of time hen rendering a static scene. For my scene however, with the volumetric effects the best results were from creating new light maps for each frame.
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