Shadow mapping
For a point light source, the view should be a perspective projection as wide as its desired angle of effect (it will be a sort of square spotlight).Because only the depth information is relevant, it is common to avoid updating the color buffers and disable all lighting and texture calculations for this rendering, to save drawing time.This depth map must be updated any time there are changes to either the light or the objects in the scene, but can be reused in other situations, such as those where only the viewing camera moves.Alternatively, culling front faces and only rendering the back of objects to the shadow map is sometimes used for a similar result.The second step is to draw the scene from the usual camera viewpoint, applying the shadow map.This scaling can be done before the perspective division, and is easily folded into the previous transformation calculation by multiplying that matrix with the following:The shadow mapping technique can also be modified to draw a texture onto the lit regions, simulating the effect of a projector.If programmable shaders are available, the depth map test may be performed by a fragment shader which simply draws the object in shadow or lighted depending on the result, drawing the scene in a single pass (after an initial earlier pass to generate the shadow map).If shaders are not available, performing the depth map test must usually be implemented by some hardware extension (such as GL_ARB_shadow), which usually does not allow a choice between two lighting models (lit and shadowed), and necessitate more rendering passes: The example pictures in this article used the OpenGL extension GL_ARB_shadow_ambient to accomplish the shadow map process in two passes.A simple way to overcome this limitation is to increase the shadow map size, but due to memory, computational or hardware constraints, it is not always possible.Notable examples of these are Percentage Closer Filtering,[7] Smoothies,[8] and Variance Shadow maps.
shadows3D computer graphicsLance Williamsz-buffertextureshadow volumesstencil bufferperspective projectionorthographic projectiondepth mapstitchingcameramatrix multiplicationcoordinate transformationOpenGLhomogeneous coordinates3D projectionDirect3DshaderprojectorshadersPhong reflection modeladditive blendingaliasingsoft shadowsShadow volumeRay castingray tracingPhoton mappingRadiosityNVidiaMarco CorbettaComputer graphicsVector graphicsDiffusion curve2D graphicsAlpha compositingLayersText-to-imageIsometric graphicsMode 7Parallax scrollingSkybox3D graphics3D renderingImage-basedSpectralUnbiasedAnisotropic filteringCel shadingFluid animationLightingGlobal illuminationHidden-surface determinationPolygon meshTriangle meshShadingDeferredSurface triangulationWire-frame modelAffine transformationBack-face cullingClippingCollision detectionPlanar projectionReflectionRenderingBeam tracingCone tracingCheckerboard renderingPath tracingScanline renderingRotationScalingShear matrixTranslationVolume renderingGraphics software3D computer graphics softwareanimationmodelingRaster graphics editorsVector graphics editorsList of computer graphics algorithms