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RENDERING BASICS

Introduction to 3D | 2006 c 2006 Gray Holland | a production of

INTERACTIVE SHADING visualization | 

Hardware Shading F

Hardware Shading is the principal tool for the evaluation of surfaces and design work. It is fully interactive, yet its speed is directly tied to the graphic performance of the given machine’s graphic card. The key is to match the Hardware Shading settings to the speed of the machine. There are 3 levels of settings that will most dramatically affect the speed of interactive shading: 1] Tessellation is the quantity of triangulation that will take place when the shading is invoked (this will be covered in more detail on the following page). The “Fast” option is a must for responsive graphic performance. “Accurate” will dramatically slow down interactively. The “Tolerance” is a factor that is relevant to the units you are working in. So in the example right, the triangulation will deviate no more than 0.01 cm from the NURBS data. 2] Shading Method is the next level of performance. Per Pixel is the high quality setting, and is necessary to show off reflections, texture maps, bump maps, etc. Per Vertex does not support the reflections, texture maps, etc., but is focused on showing off basic surface quality. It is the appropriate option for lower end graphic cards. 3] Ground Plane Settings are extra “bells and whistles” that show realistic effects of interactive shadows and reflections. It is most useful for preparing for software rendering, but it should be used sparingly because it will dramatically slow the performance of Hardware Shading (especially ground reflections). The Ground Plane option opens the shadowing and reflecting effects. Shadows produces shadows on the user defined ground plane. User Defined matches the shadows to the lighting in the scene. Shadow Blur and Transparency add realism. Reflections add more realism, but this effect is very demanding graphically. The level of Reflectivity, Depth and Blur can produce a sophisticated look and feel. Lighting Source has several useful options. “Default” has an overriding light that projects from the view camera itself. “All Lights” interactively uses the lighting you have set up in your scene.

Alt W Save Current Window [Default Panel > Windows tab]

Screen shots are great for quick presentations. The following can enhance quality captures:

• Background color can be changed to white.
• Toggle Model-gets rid of wire frame.
• Toggle Smooth –anti-alias the wire frame and shading
• Window Sync –synchronizes ortho windows for multi view shots.

TECHNICAL SHADING visualization | 

Diagnostic Shading: [Default Panel] Diagnostic Shading is a set of technical shading evaluation tools. They consist of abstract visualization of concepts, such as graphic visualizations of rate of curvature (Mean, Gaussian, Principle Minimum and Maximum) as well as stylized highlight and reflection studies (Stripe Environment, Hard Horizon, and Sky). All are very useful when evaluating high end surface development such as curvature continuous class “A” modeling...

The set of Curvature Evaluation tools includes several ways of looking at the rate of curvature on selected surfaces. These tools are designed to help highlight surface quality issues and will provide interactive feedback when manipulating surfaces. The reflection shading places surfaces in hard- edge theoretical environments to study the reflective qualities interactively. The key is that this shading is focused on

evaluation of surfaces, not about creating materials

and their assignment to objects.

BASIC LIGHTING visualization | 

Minimum Lighting Scenario: Lighting does more than just illuminate your objects: it sets the mood. And although you can add lots of lights to your scene, it’s best to keep it simple. Below is a basic layout of the minimum lighting needed to produce realistic shading and rendering of objects. Most scenes need just 3 lights: one primary directional light for overall illumination and highlights, one ambient light controlling the shadow core intensity, and one last directional light, pointing exactly opposite to the primary light, to simulate “bounced” light and delineate the resulting core shadow. Directional Light: [primary light source] This light simulates the illumination from the sun through the projection of parallel rays of light. Ambient Light: [core value] This light has the effect of ambient or defused light. It mainly determines the value of the darkest areas of objects: The core’s value. “Fill” Directional Light: [bounced light] This light simulates the bounced light which illuminates the shadow side of given objects. Primary Directional Light Ambient Light “Fill” Directional Light

Create this fill light opposite the main directional light: To accomplish this: scale a copy of the main directional light by -1 -1 - in the Informational Window (Alt Shift I). Then cool off the light’s color and reduce its intensity by half (0.5). [shadow] [highlight]

BASIC SHADING rendering | 

Diffuse: The ability of the surface to respond to light, affecting the fall off of the highlight itself. The higher the Diffuse value, the more the actual surface color realized. Thus a low value will “dull” the shader’s color, a higher value will intensify its color—material saturation control. Specular: Defines the color and intensity of surface highlights. Specular Rolloff: applies to the quality of the specularity and the ability of the surface to reflect from oblique angles. This value is often set low for shiny materials, but can be used to produce many special effects. Middle values are useful for rubber-like materials. Eccentricity: Controls the size of highlights on a surface. Small highlights define shiny surfaces like glass; large ones are used for soft or velvety surfaces such as rubber. Reflectivity: Is the ability of the surface to reflect its surroundings. Low values simulate lightly textured plastics and diffuse reflective metals like aluminum; high values work well for materials like glass, water, and chrome. Reflection: Refers to applied environmental reflection mapping only. This is most useful for Hardware Shading and RayCasting. Raytracing over-rides this channel with the scene’s Environment (unless Reflect Map parameter is turned on). The Blinn Shading Model: There are four Shading Models (Phong, Blinn, Lambert, and Lightsource). In the end Blinn is the most useful because it is the most flexible. Blinn can produce a large range of shading effects by manipulating six primary parameters (covered in detail below). Blinn has the capacity to describe diamond hard leaded glass, or velvety soft rubber, and everything in between… Diffuse > 0. Specular > 0. Specular Rolloff > 0. Eccentricity > 0. Reflectivity > 0. Diffuse > 1. Specular > 0. Specular Rolloff > 0. Eccentricity > 0. Reflectivity > 0. Diffuse > 0. Specular > 0. Specular Rolloff > 0. Eccentricity > 0. Reflectivity > 0. Diffuse > 1. Specular > 0. Specular Rolloff > 0. Eccentricity > 0. Reflectivity > 0.

TYPES OF MAPPING rendering | 

Surface, Solid, and Environment Mapping: There are 3 basic types of texture mapping. Each applies textures to channels in a different way, to achieve different effects. All of these different mapping functions can be used in different combinations to develop sophisticated material effects. Surface Mapping: This type of mapping stretches the given texture to the 4 corners of the assigned surface(s). Surface mapping takes on all the parameterization qualities of the mapped surface itself. Solid Mapping: This mapping procedure is based on the volumetric intersection of surfaces with Projection Objects. There are 8 different types of Projection Objects; each uses a different projection geometry model. The Solid texture uses the Projection Object to place itself in respect to the applied surfaces, and has the ability to move, scale, and rotate it in any way. Environment Mapping: This mapping is focused on applying reflection environments. There are several types of environments to map: Cube is used to map 6 images to create a room-like reflection. Ball and Sphere environments map images to for realistic exterior reflections. Chrome and Sky environments produce stylized procedural reflections.

Environment Maps applied directly to shaders work for Hardware Shading and Raycasting When Raytracing the Environment Map needs to be applied only to the master Environment in the Multi-lister (see page 6). Many of the Textures offered are procedural in nature. Image-based Textures include: File, Stencil, Ball, Cube, Sphere, Projection, and Volume

IMAGE MAPPING rendering | 10

Mapping A Logo: The following example covers the basics of creating a logo on a given object, based on a set of associated image files. In this case we want the color of the logo to be embossed into a metallic material. Step 1: On the selected shader, start by mapping a Solid > Projection map to the color channel. Then map a Surface > Stencil map onto its Source Texture channel. Then map a Surface > File onto its Image channel. Now you can finally Browse to map the actual color image map. Now to place the map precisely in relation on the surface itself you must first toggle on the Projection Object by clicking on the 3D texture icon. Now select that Projection Object (green cube) and transform it into position (see page 6). Step 2: Note that the surface(s) seem to be covered by repetitions of the logo (above left)—to limit the logo to just the intersection of the Projection Object, you must turn OFF the “Wrap” option under “3D Placement” (within the Solid Projection’s editor). When you are happy with the placement of this logo rename it “COLOR_project” and save out the Solid Projection map with the Multi-lister’s > Save As option. Step 3: Now add a bump map to the Bump channel by clicking its map button followed by the Browse button and selecting the recently saved color Solid Projection, then name it “BUMP_project.” Next go to this projection map’s image file and replace it with the prepared grey-scale bump map. Note that the logo now looks embossed into the metal surface (you must have Per Pixel selected in Hardware Shade to see this effect). Step 4: Now to make the logo float, you must use the Stencil feature to Mask out the area around the logo image. Go back to the Stencil map and map a Surface

File to the Mask channel, then browse for the prepared masking image. You will now notice that the result is a “floating” logo.

A negative intensity produces an embossed look, and vice versa. Color Image Map Mask Image Map Bump Image Map Multi-Channeled Shader: It is often necessary to produce several images to map to several channels to create the desired effects. This shader represents an example of this multi-dimensional use. Below is sample of the multi- lister view of this shader with all of its channels exposed. 3D Texture Icon: Toggle on and off These image files above are TIFF format prepared in Photoshop.

BASIC RENDERING rendering | 11

Global Quality Level: This field enables switching between 3 levels of rendering quality settings. Of course these settings are a default starting point and should be edited to reflect the requirements of the individual rendering. Mesh Tolerance: This controls the tesselation of objects in the render. High values are good for fast test rendering. Low values are best for final renderings, delivering fine details but longer rendering times (page 3). Anti-aliasing Levels: Anti-aliasing controls the pixel smoothness of the digital rendering. It also greatly affects rendering times. A general rule is to set the Maximum value to twice the Minimum value. 8-12 values are good settings for final renderings; 2-4 for medium tests, 1-2 for low. Raytracing Maximum Limits: This set of controls is the overhead limit for the rendering. These values can also greatly affect rendering times. EACH shader has its own settings for these values, so don’t forget to set them first (to their highest final rendering values). Then use this setting in the globals to crop limits down during test rendering (pages 13-14). Format: This is where the image format is set. TIFF is the best format because it can store alpha channel information. Render Window Selection: Allows the user to select which windows to use for rendering and whether or not to include the alpha channel (or mask). Multiple windows can be rendering and be set up at one time, but they must have exactly the same resolution. Resolution: These fields set the rendering resolution. To calculate the printable size of a given rendering, multiply your desired DPI by the image size in Inches to determine the render resolution: such as 300 DPI (8.5’ x 11’) = 2550 x 3300 pixels. Setting Up and Testing Renders: Software rendering is very much like photography. First you compose the shot. Next you adjust the placement of the lighting. Then you snap some test shots... Direct Rendering is a way to render directly into the Studio windows. In fact, you can even select just part of the window to render into. This is the place to tweak all the aspects of your rendering [composition, lighting, shaders, etc.]. Do these tests at smaller resolutions and at a Medium or Low Global Quality Level. Lastly you will want to tweak the rendering settings themselves >> [details to the right]. Final shots should be kicked off for rendering outside of Studio... Opens the Render Globals editing window Kicks off Direct Render

TRACING RAYS rendering | 1

Raytracing Concept: Raytracing works basically backwards from how rays of lights work in reality. Instead of rays of light bouncing off objects into a camera’s lens, Raytracing starts by sending rays outward from its virtual camera and traces their bounces through the objects in the scene. The image below attempts to illustrate a single ray bouncing through this sample scene. Refractions happen at points where the ray intersects transparent objects and as a result changes the angle of its path. The Refractive Index calculates the amount of refraction for any given material. The largest count of refractions in a given scene will determine the Refraction Limit needed to render effectively.

When Raytracing transparent materials each material has to be though of (and modeled) as a solid. In the case of a glass filled with a liquid, it is very important to have small offsets between the 2 materials, such as liquid and glass. This assures correct Raytracing of the materials and avoids potential tessellation artifacts. This ray trace reveals that it would take a Refraction Limit of at least 8 to see the floor just behind the glass through all of its refracted bounces (the Refract Limit is set per shader page 6, and in the Render Globals page 11). Just to be safe, you might want to add 2 more to the Refractive Limit to achieve the best render results... The Shadow Limit is linked to the Refract Limit: for shadows to be rendered properly the Shadow Limit is always 1 less than the Refract Limit (Shader page 6, Globals page 11).

rendering | 1

Refractions Limits: Setting the Reflection, Refraction, and Shadow Limits are some of the most confusing aspects of Raytracing. Setting them too low will not look realistic, setting them too high will drive rendering times high. The illustrations on this page hopefully with help guide you through setting up these limits “just right.”

RAYTRACING REFRACTION SETTINGS

Reflect Limit 2 Refract Limit 10 Shadow Limit 9 Soft Shadow 2 Reflect Limit 2 Refract Limit 4 Shadow Limit 3 Reflect Limit 2 Refract Limit 8 Shadow Limit 7 Reflect Limit 1 Refract Limit 2 Shadow Limit 1 Reflect Limit 2 Refract Limit 6 Shadow Limit 5 Hardware Shade with shadows Reflect Limit 2 Refract Limit 10 Shadow Limit 9 Soft Shadow 12

The Shadow Limit is always set 1 less than the Refraction Limit (page 6 and page 11). Rarely are reflections needed past 2, too many reflections often make shots messy. Final rendering with all the tweaked settings ends up taking 16:27 minutes to render at a 600 X 460 resolution. Setting Shadow Samples to around 12 will most often give you fairly smooth Soft Shadows, but will drive up render times; use 2 for test renders.