《3D游戏编程》随书光盘 12章: 设计阴影的多种技巧

//----------------------------------------------------------------------------- // Name: ShadowVolume Direct3D Sample // // Copyright (c) Microsoft Corporation. All rights reserved. //----------------------------------------------------------------------------- Description =========== The ShadowVolume sample uses stencil buffers to implement real-time shadows. In the sample, a complex object is rendered and used as a shadow-caster, to cast real-time shadows on itself and on the terrain below. Stencil buffers are a depth buffer technique that can be updated as geometry is rendered, and used again as a mask for drawing more geometry. Common effects include mirrors, shadows (an advanced technique), dissolves, etc.. Note that not all cards support all features for all the various stencil buffer techniques (some hardware has no, or limited, stencil buffer support). For more information on stencil buffers, refer to the DirectX SDK documentation. Path ==== Source: DXSDK\Samples\C++\Direct3D\StencilBuffer\ShadowVolume Executable: DXSDK\Samples\C++\Direct3D\Bin User's Guide ============ The following keys are implemented. The dropdown menus can be used for the same controls. <Enter> Starts and stops the scene <Space> Advances the scene by a small increment <F1> Shows help or available commands. <F2> Prompts user to select a new rendering device or display mode <Alt+Enter> Toggles between fullscreen and windowed modes <Esc> Exits the app. Programming Notes ================= Real-time shadows is a fairly advanced technique. Each frame, or as the geometry or lights in the scene are moves, an object called a shadow volume is computed. A shadow volume is an actual 3D object which is the siholuette of the shadowcasting object, as pretruded away from the light source. In this sample, the 3D object which casts shadows is a bi-plane. Each frame, the sihlouette of the plane is computed (using an edge detection algorithm, in which sihlouette edges are found because the normals of adjacent polygons will have opposing normals with respect to the light vector). The resulting edge list (the sihlouette) is pretuded into a 3D object away from the light source. This 3D object is known as the shadow volume, as everypoint inside the volume is inside a shadow. Next, the shadow volume is rendering into the stencil buffer twice. First, only forward-facing polygons are rendering, and the stencil buffer values are incremented each time. Then the back-facing polygons of the shadow volume are drawm, decrementing values in the stencil buffer. Normally, all incremented and decremented values would cancel each other out. However, because the scene was already rendered with normal geometry (the plane and the terrain, in this case), some pixels will fail the zbuffer test as the shadowvolume is rendered. Any values left in the stencil buffer correspond to pixels that are in the shadow. Finally, these remaining stencil buffer contents are used as a mask, as a large all-encompassing black quad is alpha-blended into the scene. With the stencil buffer as a mask, only pixels in shadow are darkened This sample makes use of common DirectX code (consisting of helper functions, etc.) that is shared with other samples on the DirectX SDK. All common headers and source code can be found in the following directory: DXSDK\Samples\C++\Common