Antialiasing¶

VisualRealism¶

• View(persective)
• Field of view(proper clipping)
• Omit hidden parts
• Surface details like texture
• Light effects on surfaces like continuous shading,shadows and caustics

• Visible Surface Determination
• Goal
• Given: a set of 3D objects and view specification
• Determine: those parts of the objects that are visible when viewed along the direction of projection
• Or, equivalently, elimination of hidden parts(hidden lines and surfaces)

• Visible parts will be drawn/shown with proper shading

• Approaches

• Object space methods
  • Object precision
• Image space methods
  • Image precision

• z-buffer algorithm

• Object precision

• for(each object in this world){determine the parts of the object whose view is unobstructed by other parts or any other object;drawthoseparts;}
• Image Precision Algorithm

• for(each pixel in the image){ 画出最近的 pixel}

• Back-face Culling：背面是不可能被看到的。怎么做？ 1. Find angle between the eye-vector & normal to face 2. If the angle is between 0 and 90 degrees, discard the face

If the scene consists of a single closed convex polygonal surface,then back-face culling is equivalent to hidden surface removal.

• Painter's Algorithm: Back to Front
• Warnock's Area Algorithm: Divide and Conquer

Z-buffer Algorithm¶

• Apart from a frame buffer F in which color values are stored.
• it also needs a z-buffer, of the same size as frame buffer,to store depth(z) values. 存的是离得最近的深度值，z 值更小的就是离得更近的

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for(j=0;j<SCREEN_HEIGHT;j++)
{
    for(i=0;i<SCREEN_WIDTH;i++)
    {
        WriteToFrameBuffer(i,j,BackgroundColor);
        WriteToZBuffer(i,j,MAX_DEPTH);
    }
}
for(each polygon)
    for(each pixel in the polygon projection)
    {
        z = polygon.z at (i,j);
        if(z < ReadFromZBuffer(i,j))
        {
            WriteToFrameBuffer(i,j,polygon.color);
            WriteToZBuffer(i,j,z);
        }
    }

如果更小就更新，因为更近。越深越近

• Binary Space Partitioning Trees:BSP Tree
• Very efficient for static group of 3D polygons as seen from an arbitary viewpoint
• Correct order for Painter's Algorithm is determined by a traversal of the binar tree of polygons

Aliasing¶

采样率 / 分辨率不够，看到锯齿

Anti-aliasing: 降低锯齿

• Super-samping: 一个 sampling 取不止一个点，增加采样率
• Area sampling: