If you want to draw a large brick wall without texture mapping, for example, each brick must be drawn as a separate polygon. Without texturing, a large flat wall - which is really a single rectangle - might require thousands of individual bricks, and even then the bricks may appear too smooth and regular to be realistic.
If you're designing a mechanical part made from smaller three-dimensional pieces, you often want to display regions where the pieces overlap.
In many cases, such regions indicate design errors where parts of a machine interfere with each other. In the case of moving parts, it can be even more valuable, since a search for interfering regions can be done through a complete mechanical cycle of the design.
The method for doing this is complicated, and the description here might be too brief. Complete details can be found in the paper Interactive Inspection of Solids: The method is related to the capping algorithm described in "Stencil Test" in Chapter The idea is to pass an arbitrary clipping plane through the objects that you want to test for interference, and then determine when a portion of the clipping plane is inside more than one object at a time.
For a static image, the clipping plane can be moved manually to highlight interfering regions; for a dynamic image, it might be easier to use a grid of clipping planes to search for all possible interferences. Draw each of the objects you want to check and clip them against the clipping plane.
Note which pixels are inside the object at that clipping plane using an odd-even count in the stencil buffer, as explained in the preceding section.
For properly formed objects, a point is inside the object if a ray drawn from that point to the eye intersects an odd number of surfaces of the object.
To find interferences, you need to find pixels in the framebuffer where the clipping plane is in the interior of two or more regions at once; in other words, in the intersection of the interiors of any pair of objects.
If multiple objects need to be tested for mutual intersection, store 1 bit every time some intersection appears, and another bit wherever the clipping buffer is inside any of the objects the union of the objects' interiors.
For each new object, determine its interior, find the intersection of that interior with the union of the interiors of the objects so far tested, and keep track of the intersection points. Then add the interior points of the new object to the union of the other objects' interiors.
You can perform the operations described in the preceding paragraph by using different bits in the stencil buffer together with various masking operations. Three bits of stencil buffer are required per pixel - one for the toggling to determine the interior of each object, one for the union of all interiors discovered so far, and one for the regions where interference has occurred so far.
You can find intersections and unions of the bits in the stencil buffers using the stenciling operations.
For example, to make bits in buffer 2 be the union of the bits in buffers 1 and 2, mask the stencil to those 2 bits, and draw something over the entire object with the stencil function set to pass if anything nonzero occurs. This happens if the bits in buffer 1, buffer 2, or both are turned on.
If the comparison succeeds, write a 1 in buffer 2. Also, make sure that drawing in the color buffer is disabled. An intersection calculation is similar - set the function to pass only if the value in the two buffers is equal to 3 bits turned on in both buffers 1 and 2. Write the result into the correct buffer.
See "Stencil Test" in Chapter OpenGL Programming Guide: Programming Guide > Chapter 4 Chapter 4 Color. Chapter Objectives. The goal of almost all OpenGL applications is to draw color pictures in a window on the screen. The window is a rectangular array of pixels, each of which contains and displays its own color.
Thus, in a sense, the point of all the calculations. Welcome to the OpenGL® ES Programming Guide Website. This is the official website for the OpenGL® ES Programming vilakamelia.com on this site you can find information on where to download all of the sample code from the book as well as links to the errata.
If you don't already own the book and are interested in purchasing it, you can purchase the book on Safari or vilakamelia.com OpenGL Programming Guide: Programming Guide > Chapter 3 Chapter 3 Viewing.
Chapter Objectives. After reading this chapter, you'll be able to do the following: View a geometric model in any orientation by transforming it in three-dimensional space;. Before issuing a command to clear multiple buffers, you have to set the values to which each buffer is to be cleared if you want something other than the default .
OpenGL Programming Guide: OpenGL Programming Guide The Official Guide to Learning OpenGL, Version About This Guide; Chapter 1. Introduction to OpenGL; Chapter 2. State Management and Drawing Geometric Objects; Chapter 3.
Viewing; Chapter 4. Color; Chapter 5. Lighting; Chapter 6. Khronos SIGGRAPH BOF Sessions LiveStreaming. The Khronos Group BOF sessions are being held today at SIGGRAPH All of the sessions will be live streamed with details on all the sessions available on the Khronos SIGGRAPH event vilakamelia.comns will cover glTF, OpenXR, WebGL, Vulkan and OpenGL.