How to render models and particles in MAYA at the same time?

Maya hardware rendering particles combined with software rendering elements.

Hardware rendering particles

stash

Hide particles before hardware rendering. If there is no concealment, motion blur will not produce correct results, and the picked frame will not match the original frame.

Alpha channel

When the transparency value of the wizard is less than 1, the Alpha channel generated by the hardware rendering buffer is incorrect. Unlike the color channel, considering the color of the particles behind the current particle, the Alpha channel will return the value of the final particle only displayed on the display-this means that if you have 1000 particles stacked together, the transparency value of each particle is 0. 1, even if you can't see through the particle pile in 3D view, cg/image/ will put a 0.6544 in the final Alpha channel of the image.

Using brightness as the Alpha channel will produce incorrect results. With the brightness of the particle, you will delete all the shadows in the particle. No matter where the dark areas are, the dark areas will be more transparent than the bright areas. The final image looks flat and the dust has almost no texture.

The best way to synthesize particles is to render with non-embedded Alpha channel, and the background should be 100% green. Using simple synthesis technology, this green screen method, the alpha channel will have accurate results. If the particles have no green information, this method will be better, which is why we limit the color range of dust particles to between green and red, rather than through the green range.

Geometric mask

Since most particle effects are usually three-dimensional elements with volume, a simple two-dimensional Alpha channel is not enough when your effects are layered correctly. Volumes have different densities at different depths, so you need to cut the volume in three-dimensional space so that the volume in front of the element will maintain the density. There are two ways:

Open the geometry mask, cg/image/ automatically use all the geometry in the scene as a three-dimensional cutting picture. This geometry is used to cut particles, but it is not visible in the color and Alpha channels, just like using background materials in software rendering.

Special mask element

One consequence of using geometric masks is that if you replace particles and replace geometry, the geometry will also be masked, but it will not appear in the color or Alpha channel. In order to avoid this situation, you can specify a Lambert material for all the geometry used as a mask in the scene, whose color and incandescence are 100% green, or other colors, as long as you can set keyframes in the future. The reason to increase or decrease the percentage to 100% green is to eliminate any influence of hardware shadow on geometry.

Matching mosaic

When using NURBS geometry in the scene, it is very important that the mosaic subdivision in the three-dimensional view should match the rendered mosaic subdivision rendered by software. The NURBS object of cg/image/ is displayed in the viewport with high precision-hotkey: 3-which is different from rendering mosaic subdivision with renderer. If you are rendering a very thick volume, you will see that the geometric mask has more facets than the software rendering object, which leads to unpleasant edges around the object when it is synthesized. To avoid this, turn on Show Render Subdivision for all NURBS objects in the scene. Now, when you render the hardware, the tessellation will match the software renderer.

Motion blur

Motion blur is necessary when simulating rendering particles. Generally speaking, particles are small and move quickly. The appearance of particle system not only refers to color, light and transparency, but also includes the fuzzy state of particles in motion. Motion blur not only reflects the particle velocity, but also reflects the particle volume. A whirlwind doesn't need to be composed of100,000,000 fast rotating point particles, and hundreds of sprite with motion blur can also produce the same wonderful effect.

The motion blur of hardware rendering is different from that of software rendering, so there is no need to consider how difficult it is to match them. In fact, it is impossible to achieve 100% accuracy, and it is lucky to achieve 50% accuracy. Depending on the moving speed of the object relative to the camera, the result may be acceptable or completely useless. Different synthesis techniques and subordinate paths of particle systems can be used to eliminate these differences.

In order to better match the software rendering of particles, the length of motion blur should be set to match the shutter angle of the camera. Shutter angle of 144 will produce motion blur of 144/360 or 0.4. If you use a higher value, you may get interesting results. It is important to remember the following points:

If a geometric mask is used, setting the motion blur too high or too low will lead to the mismatch between the mask and the software motion blur.

If your camera is animated and the motion blur setting is higher than 1, your effect will swim in three-dimensional space, and the motion blur result will be before the time axis.