BBC Basic：无法在屏幕上绘制矩形 [英] BBC Basic: Cannot plot rectangle on screen

问题描述

我最近在BBC Micro（B型）上得到了手，并且一直在玩它作为一个业余爱好项目。

我遇到了一些麻烦图形命令，并想知道是否有人可以指出我在正确的方向...我写了下面的测试程序，在屏幕上画一个矩形：

  10 CLS 
 20 MODE 5 
 30 MOVE 0,0 
 40 PLOT 97,100,100 
  

当我运行这个程序时，程序完成，但没有绘制矩形（我可以看到）。我使用同轴电缆连接到CRT电视，但我不相信光标正在屏幕外显示，因为我试着调整X / Y值来检查这一点。

我在测试程序中犯了错误吗？是否可能存在已知的硬件故障，我应该检查一下？解析方案

有一个简单的解释：PLOT 97（绘制矩形）是没有在原来的BBC微型模型B上实现 - 它使用的PLOT代码只能达到87.我不能完全确定何时引入PLOT 96-103，它可能是Model B +或BBC Master。

在模型B上，您必须将矩形绘制为两个三角形（这里位于屏幕的中心）：

  10模式5 
 20 MOVE 592,462 
 30 PLOT 0,0,50 
 40 PLOT 81,50，-50 
 50 PLOT 81,0,50 
  

Richard。

I recently got my hands on a BBC Micro (model B), and been playing around with it as a hobby project.

I'm having some trouble with the graphics commands, and was wondering if anyone could point me in the right direction... I have written the following test program to draw a rectangle on the screen:

10 CLS
20 MODE 5
30 MOVE 0,0
40 PLOT 97,100,100

When I run this, the program completes but no rectangle is drawn (that I can see). I'm using a coaxial cable to connect to a CRT TV, but I don't believe the cursor is drawing off-screen because I've tried adjusting the X/Y values to check for this.

Have I made a mistake in my test program? Is there possibly a known hardware fault that I should check for?

解决方案

There's a simple explanation: PLOT 97 (draw rectangle) was not implemented on the original BBC Micro Model B - that used PLOT codes only up to 87. I'm not absolutely certain when PLOT 96-103 were introduced, it may have been the Model B+ or the BBC Master.

On a Model B you must draw the rectangle as two triangles (here in the centre of the screen):

   10 MODE 5
   20 MOVE 592,462
   30 PLOT 0,0,50
   40 PLOT 81,50,-50
   50 PLOT 81,0,50

Richard.

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