The Compositing Buffer: A Flexible Method for Image Generation and Image Editing

In this paper, we describe a new buffer architecture called the Compositing Buffer. Although it is based on the A-buffer architecture described by Carpenter¹, the new architecture introduces two important ideas which make image generation more flexible. The first idea is the storing of bitmask index instead of the bitmask. This allows accurate images to be generated while at the same time, minimising memory usage. The second idea is the introduction of the concept of dynamic object. This allows images to be edited interactively. Applications of the two ideas will also be discussed in the paper.     

Applying Rounding-Up Integral Linear Interpolation to the Scan-Conversion of Filled Polygons

This paper is motivated by a special linear interpolation problem encountered in scan-line algorithms for scan-conversion of filled polygons. rounding-up integral linear interpolation is defined and its efficient computation is discussed. The paper then incorporates rounding-up integral linear interpolation into a scan-line algorithm for filled polygons, and it discusses the implementation of the algorithm. This approach has the advantage of only requiring integer arithmetic in the calculations. Furthermore, the approach provides a unified treatment for calculating span extrema for left and right edges of the polygon that guarantees the mutual exclusiveness of the ownership of boundary pixels of two filled polygons sharing an edge.     

有效的混合圆弧扫描转换算法

为了提高直线和曲线的光栅转换速度而产生了多步算法和行程算法.论文分析了光栅圆弧的特性,利用对中点法的结构和决策参数的重新构造,提出了一种简单、快速的行程计算方法.该方法以2点步进为主进行行程计算,并可以容易地结合局部模式分析以处理复杂的光栅模式.实验和分析表明,所形成的新算法综合利用了2点步进和行程方法的优势,有效地减少了计算量和I/O次数,其圆弧绘制速度明显优于现有其它算法,且理论推导简单,不含乘法、开方等复杂运算,硬件实现容易,并可以推广到其他圆锥曲线的绘制.     

Approximate Line Scan-Conversion and Antialiasing

This paper presents an approximate multiple segment line scan-conversion method — the Slope Table Method. The statistics show that the new method can increase the percentage of multiple segment lines (i.e., lines with more than one segment) in an N×N raster area from about 39% to more than 99%. In software implementation for scan-conversion and antialiasing of randomly generated lines, this method is on average more than 6 times faster than Gupta's antialiasing line algorithm. Compared with other line scan-conversion methods, the method may choose pixels which are not the closest to the line (i.e., error pixels). Here the paper demonstrates that the visual effect is acceptable in most applications with the error pixels.     

反走样直线的灰度循环生成算法

灰度转换是整数反走样直线和曲线绘制算法中较为耗时的操作.为了提高反走样直线的绘制效率,提出了一种直接利用灰度循环控制生成反走样直线的纯整数算法.该算法采用两点反走样模式,根据对灰度值的分解、每次步进时的像素及其灰度值直接利用灰度增量控制产生,从而避免了候选点与真实直线之间的距离计算,以及由距离到灰度的转换.分析表明,该算法每次步进仅需要4～5次整数基本运算,其效率较现有整数反走样直线生成算法有大幅度提高,且具有与基本直线生成算法相似的简单性.     

基于类最佳逼近的三步直线生成算法

文章提出一种新的直线逼近方法——类最佳逼近，基于这种逼近方法，斜率k∈[0，0．5）的直线和斜率为1-k的直线具有某种互补性质。利用该性质，设计出一种新的三步直线方法，该算法揭示了直线计算的互补性，理论简单，精度达到最好。最后比较了该算法和直线的双步算法，Brensenham算法。指出新算法改善了Breserham算法和双步算法的计算效率。该算法对于硬件实现将更有益处。     

多段扫描转换直线算法

在探讨直线扫描转换的对称性和多段性的基础上，提出一种基于多段扫描转换的直线扫描转换算法。该算法用简单的像素段复制或并行填充各段像素替代逐点计算，有效地降低了计算花费,加快了扫描转换速度。     

Event Reports

Second Eurographics Workshop on Parallel Graphics and Visualization, Rennes, France September 24–25, 1998     

基于最佳逼近的以段为步长的直线算法

证明了直线在最佳逼近中的与下逼近不同的一些性质。然后利用这些性质,提出了基于最佳逼近的以段为步长的直线算法。该算法和基于下逼近的以段为步长的算法相比,既保持了计算效率,又提高了计算精度。理论分析表明该算法效率优于Brensenham、双步、三步、四步等直线算法。图形设备的硬件层实现该算法将更加有效。     

有效的混合圆弧扫描转换算法

为了提高直线和曲线的光栅转换速度而产生了多步算法和行程算法。论文 分析了光栅圆弧的特性,利用对中点法的结构和决策参数的重新构造,提出了一种简单、快 速的行程计算方法。该方法以2 点步进为主进行行程计算,并可以容易地结合局部模式分析 以处理复杂的光栅模式。实验和分析表明,所形成的新算法综合利用了2 点步进和行程方法 的优势,有效地减少了计算量和I/O 次数,其圆弧绘制速度明显优于现有其它算法,且理论 推导简单,不含乘法、开方等复杂运算,硬件实现容易,并可以推广到其他圆锥曲线的绘制。