Raytrace Rendering Maya 2013

Transcription

1 Michael O'Rourke Raytrace Rendering Maya 2013 Concept Raytracing calculates the bouncing of light from one object to another This bouncing of the light beams yields very accurate renderings of shiny and transparent objects -- for example, reflections, refractions, and transparency (A simpler algorithm is raycasting, which does not bounce light from one object to another Raycasting does not yield such accurate reflections and transparency but it can render them, through various tricks Because it is simpler, raycasting can be much faster than raytracing See the Raycast Rendering tutorial in this set) By default, Maya rendering does not use raytracing because it is more complex and slower

2 Usually, you use raytracing only if you need its special visual effects -- that is, reflections, refractions, or accurate transparency Set up Model a ground plane and one or two simple objects sitting on or just above it Make a simple directional light Not too bright If it s really bright, it will wash out any reflections Enabling Raytracing First you must turn on raytracing, which is off by default Go to the Rendering module >Window > Rendering Editors >Render Settings At the top of the window, Render using = Maya Software Go to the Maya Software tab > Raytracing Quality (Third tab down) Check on Raytracing Numbers for Reflections, Refractions and Shadows = number of rays that will be traced for the calculation of each of these phenomena Higher numbers => greater quality => longer rendering time Use the defaults for now Reflections (See the color illustration at the top of the page) To make an object reflective, >Window >Rendering Editors >Hypershade >Create >Materials Create either a Blinn, or a Phong material that is, one that is shiny and could be reflective

3 Do not use Lambert, because Lambert has zero specularity -- that is, zero shininess Make the color a light color so it will be easier to see reflections Do not make the material transparent for the same reason Double-click the material s icon to open its Attribute Editor >Specular Shading > Reflectivity WARNING: Reflectivity is 0.5 by default for both Phong and Blinn materials that is, all objects with any specularity are automatically set to be 50% reflective Adjust the Reflectivity value Try about 0.8 to start Test render your scene >Render >Render Current Frame This will use whatever setting you set in the Render Settings Since you turned on Raytracing in the Render Settings, the Render View window will use raytracing Your rendering should show reflections If it doesn t, Make sure the reflected objects are close enough to the reflective surface Make sure the reflected surfaces are well lit If they are extremely dark, they will not be visible as reflections If you know that a particular object will not be visible as reflections (for example, because it is too far away), you can save rendering time by telling the software not to think about it in its reflection calculations >Window >Rendering Editors >Rendering Flags

4 Show: Objects (upper left of window) Click on the name of shape node for your object CAREFUL: you must select the shape node For example, nurbscylindershape1 In the right panel, Visible in Reflections = Off (alternatively, = 0) Transparency To make an object transparent, In the Hypershade window, Double-click on the material s icon to open its Attribute Editor >Common Material Attributes > Transparency Adjust the slider to get more or less transparency Default is no transparency at all Render a test frame Your object should now render as transparent (NOTE: both raytracing and raycasting can render transparency) Refractions (See the black & white illustration at the top of the page) When light passes through a transparent object, the light bends a little This is called the refraction of light By default, Maya does not render refractions because they require extra calculations WARNING: Even after you have turned on raytracing, refractions are off by default Model a NURBS sphere Light will refract more through a curved surface than a straight Model a stretched cube behind it So we will be able to see the straight lines of the cube bend with the refracted light

5 Refractions are assigned per Material >Window >Hypershade Double-click on your material to open its Attribute Editor Make sure the material has transparency (Refractions are only possible with transparent objects) >Raytrace Options Check on Refractions Change the number for Refractive Index This is the parameter that controls how much the light bends It is derived from real-world numbers used in Physics Default = 1.0 that is, no bending of light at all This is what happens in clear air TIP: Refractive index numbers are usually extremely close to for example, 0.93, or 1.07 Larger changes make the light bend in very unrealistic ways Try 1.1 for your first test If you know that certain objects will not be visible as refractions (for example, because they are too far away), you can save rendering time by telling the software not to think about them Same procedure as above for reflections: >Window >Rendering Editors >Rendering Flags Show: Objects (upper left of window) Click on the name of shape node for your object For example, nurbscylindershape1 In the right panel, Visible in Refractions = Off (alternatively, = 0)

6 Shadows Transparent objects should cast transparent shadows, because not all the light is being blocked by the object The raycasting algorithm always renders opaque shadows, even if your object is transparent You need to use raytracing to get transparent shadows See the Cast Shadows tutorial in this set IPR Rendering - Warning The IPR rendering method does not support raytracing It only renders with the raycast renderer If you do an IPR rendering of a raytraced scene, it will render it as a raycast rendering, and give you an warning message at the bottom of the screen All raytraced renderings must be done with either: >Render >Render Current Frame or >Render >Batch Render