关键词: 阴影图, 软阴影, 投影, 可见因子, 半影

Abstract: A real-time soft shadow mapping algorithm based on backprojection is presented to generate real-time shadows.The algorithm uses a single shadow map per light source，and treats the shadow map as a simple discretized representation of the scene.Also，a visibility factor is introduced to calculate the percentage of light seen by a single pixel in the scene and some other solutions are proposed to accelerate the efficiency of rendering，such as fragment shader with GPU，a Hierarchical Shadow Map（HSM），adaptive precision，and so on.The experimentation shows that the algorithm is well suited to render both complex and dynamic scenes.It naturally handles occluder fusion in particular，and maps well to programmable graphics hardware.

Key words: shadow maps, soft shadow, projection, visibility factor, penumbra