Direct2D - 保留现有内容并覆盖新值 [英] Direct2D - preserve the existing content and overwrite the new values

问题描述

我计划为我的应用程序开发 XY 绘图仪.为了给出一些基本的想法，它应该是什么样子(当然实现会有所不同)，请参考 此处 和此处.

I am planning to develop a XY Plotter for my application. To give some basic idea, how it should look like (of course the implementation would be different), please refer here and here.

在模拟过程中(假设完成模拟需要 4 小时)，在固定的 X 轴上，新的 Y 值应该(覆盖).

During the simulation (let's assume, it takes 4 hours to complete the simulation), on a fixed X axis, the new Y values should be (over)written.

但是，Direct2D 的问题在于，每次调用 pRenderTarget->BeginDraw() 时，都会删除现有的绘图(/Plot/BitMap/Image 等)并生成一个新图像正在绘制.因此我会失去旧的价值观.

But, the problem with Direct2D is that, every time pRenderTarget->BeginDraw() is called, the existing Drawing(/Plot/BitMap/Image, etc) is deleted and a new image is being drawn. Therefore I would lose the old values.

当然，我总是可以在缓冲区/变量中缓冲旧的 Y 值，并在下一个绘图中使用它.但是，模拟运行了 4 个小时，不幸的是我无法保存所有的 Y 值.这就是为什么我需要在现有的目标图像/绘图/等上渲染/绘制新的 Y 值.

Of course, I can always buffer the old Y values in a buffer/variable and use it in the next drawing. But, the simulation runs for 4 hours and unfortunately I can't afford to save all the Y values. That's why, I need to render/draw the new Y values on the existing target-image/plot/etc.

而且，如果在一定时间内不调用 pRenderTarget->EndDraw()，我的应用程序将因资源限制而崩溃.

And, If don't call pRenderTarget->EndDraw() within a definite amount of time, my application would crash due to resource constraints.

如何防止这个问题并达到要求?

How do I prevent this problem and achieve the requirement?

推荐答案

您要问的是一个相当复杂的要求 - 它比看起来更困难！Direct2D 是一个 立即模式绘图API.您在即时模式图形中绘制到屏幕上的内容没有状态维护或持久性.

What you're asking is quite a complex requirement - it's more difficult than it appears! Direct2D is an Immediate-Mode drawing API. There is no state maintenance or persistence of what you have drawn to the screen in immediate mode graphics.

在大多数即时模式图形 API 中，都有裁剪和脏矩形的概念.在 Direct2D 中，您可以使用这三种技术之一来绘制屏幕的子集.将屏幕外渲染到位图和双缓冲可能是一个很好的尝试技术.例如你的流程变成:

In most immediate-mode graphics APIs, there is the concept of clipping and dirty rects. In Direct2D you can use one of these three techniques to draw to a subset of the screen. Rendering offscreen to bitmap and double-buffering might be a good technique to try. e.g. your process becomes:

• 绘制到离屏位图
• 点阵位图到屏幕
• 在新数据上，绘制到新位图/与现有位图结合

只有当您添加新数据/绘图时，您的绘图没有滚动或更改比例时，此技术才有效.

This technique will only work if your plot is not scrolling or changing in scale as you append new data / draw.

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