背景:

有时需要在屏幕上绘制一个像素框,并拾取框框内的图元或者vtkCell, 然后翻阅了VTK源码,做了摘抄并且提取了关键绘制代码

结果以及关键代码:

	{
#if 0
				//获取整个窗口的宽高。。。。  pixels 开辟的内存大小，是整个屏幕宽高的大小。 然后将 start-end 之间的矩形内容进行渲染....

				if (!PixelArray) PixelArray = vtkUnsignedCharArray::New();
				PixelArray->Initialize();
				PixelArray->SetNumberOfComponents(4);


				int* size = Interactor->GetRenderWindow()->GetSize();
				PixelArray->SetNumberOfTuples(size[0] * size[1]);

				//GetRGBACharPixelData 获取该像素范围内的RGBA值？

				int StartPosition[2]{ 0,0 };
				//int EndPosition[2]{ size[0]*0.7, size[1] * 0.7 };
				int EndPosition[2]{ 150,120 };

				vtkUnsignedCharArray* tmpPixelArray = vtkUnsignedCharArray::New();
				tmpPixelArray->DeepCopy(PixelArray);
				unsigned char* pixels = tmpPixelArray->GetPointer(0);

				int min[2], max[2];

				min[0] = StartPosition[0] <= EndPosition[0] ?
					StartPosition[0] : EndPosition[0];
				if (min[0] < 0) { min[0] = 0; }
				if (min[0] >= size[0]) { min[0] = size[0] - 1; }

				min[1] = StartPosition[1] <= EndPosition[1] ?
					StartPosition[1] : EndPosition[1];
				if (min[1] < 0) { min[1] = 0; }
				if (min[1] >= size[1]) { min[1] = size[1] - 1; }

				max[0] = EndPosition[0] > StartPosition[0] ?
					EndPosition[0] : StartPosition[0];
				if (max[0] < 0) { max[0] = 0; }
				if (max[0] >= size[0]) { max[0] = size[0] - 1; }

				max[1] = EndPosition[1] > StartPosition[1] ?
					EndPosition[1] : StartPosition[1];
				if (max[1] < 0) { max[1] = 0; }
				if (max[1] >= size[1]) { max[1] = size[1] - 1; }

				int i;

				//防止数据超过255 0 200 两个循环，刚好给 RGBA 赋值..... 这里是绘制了四条边
				int centY = (min[0] + max[0]) / 2;
				for (i = min[0]; i <= max[0]; i++)
				{
					//下边
					pixels[4 * (min[1] * size[0] + i)] = 255 ^ pixels[4 * (min[1] * size[0] + i)];
					pixels[4 * (min[1] * size[0] + i) + 1] = 1 ^ pixels[4 * (min[1] * size[0] + i) + 1];
					pixels[4 * (min[1] * size[0] + i) + 2] = 1 ^ pixels[4 * (min[1] * size[0] + i) + 2];

					//中间一条直线.
					pixels[4 * (centY * size[0]) + i] = 255 ^ pixels[4 * (centY * size[0]) + i];
					pixels[4 * (centY * size[0] + i) + 1] = 255 ^ pixels[4 * (centY * size[0] + i) + 1];
					pixels[4 * (centY * size[0] + i) + 2] = 255 ^ pixels[4 * (centY * size[0] + i) + 2];

					//上边
					pixels[4 * (max[1] * size[0] + i)] = 1 ^ pixels[4 * (max[1] * size[0] + i)];
					pixels[4 * (max[1] * size[0] + i) + 1] = 255 ^ pixels[4 * (max[1] * size[0] + i) + 1];
					pixels[4 * (max[1] * size[0] + i) + 2] = 1 ^ pixels[4 * (max[1] * size[0] + i) + 2];
				}
				std::cout << "x i: " << i << endl;
				for (i = min[1] + 1; i < max[1]; i++)
				{
					pixels[4 * (i * size[0] + min[0])] = 1 ^ pixels[4 * (i * size[0] + min[0])];
					pixels[4 * (i * size[0] + min[0]) + 1] = 1 ^ pixels[4 * (i * size[0] + min[0]) + 1];
					pixels[4 * (i * size[0] + min[0]) + 2] = 255 ^ pixels[4 * (i * size[0] + min[0]) + 2];

					pixels[4 * (i * size[0] + max[0])] = 255 ^ pixels[4 * (i * size[0] + max[0])];
					pixels[4 * (i * size[0] + max[0]) + 1] = 1 ^ pixels[4 * (i * size[0] + max[0]) + 1];
					pixels[4 * (i * size[0] + max[0]) + 2] = 255 ^ pixels[4 * (i * size[0] + max[0]) + 2];
				}

				std::cout << "y i: " << i << " " << min[0] << " " << min[1] << " " << max[0] << " " << max[1] << endl;
				Interactor->GetRenderWindow()->SetRGBACharPixelData(0, 0, size[0] - 1, size[1] - 1, pixels, 0);

				Interactor->GetRenderWindow()->Frame();

#elif 0


				/// <summary>
				/// 这里就这样吧。。不就结了..
				/// </summary>
				if (!PixelArray) PixelArray = vtkUnsignedCharArray::New();
				int w = 150;
				int h = 120;
				auto length = [=]() {

					return w * h;
				};
				int length2 = w * h;
				int componets = 4;
				PixelArray->SetNumberOfTuples(length2);
				PixelArray->SetNumberOfComponents(componets);
				vtkUnsignedCharArray* tmpPixelArray = vtkUnsignedCharArray::New();
				tmpPixelArray->DeepCopy(PixelArray);
				unsigned char* pixels = tmpPixelArray->GetPointer(0);

				//赋值给数组pixels
				int controls = length2;
				//std::cout << "总大小: " << sizeof(pixels)/ sizeof(char) << endl;
				std::cout << "验证了Pixels大小是获取正确的..." << "controls: " << controls << "  tmpPixelArray: " << tmpPixelArray->GetNumberOfTuples() << endl;

				//正确的找到 X Y 的坐标数值.
				/*int stripStep = w ;
				for (size_t i = 0; i < controls - stripStep; i+=stripStep)
				{
					for (size_t j = 0; j < stripStep-4; j += 4)
					{
						pixels[i+j] = 255;
						pixels[i+j + 1] = 255;
						pixels[i+j + 2] = 0;
					}
				}*/
				/*for (size_t i = 0; i < controls; i += 4)
				{
					pixels[i ] = 255;
					pixels[i  + 1] = 0;
					pixels[i  + 2] = 0;

					pixels[i+4] = 255;
					pixels[i+4 + 1] = 0;
					pixels[i+4 + 2] = 0;

				}*/
				for (size_t i = 0; i < w; i++)
				{
					pixels[i] = 255;
					pixels[i + 1] = 0;
					pixels[i + 2] = 0;

					//第二行而已...
					pixels[i * w] = 255;
					pixels[i * w + 1] = 0;
					pixels[i * w + 2] = 0;

					pixels[i * w * 2] = 255;
					pixels[i * w * 2 + 1] = 0;
					pixels[i * w * 2 + 2] = 0;

					/*	pixels[i * w] = 255;
						pixels[i * w + 1] = 0;
						pixels[i * w + 2] = 0;*/

				}

				//或者这个.
				Interactor->GetRenderWindow()->SetRGBACharPixelData(0, 0, w - 1, h - 1, pixels, 0);//注意这里的RGBA

				Interactor->GetRenderWindow()->Frame();

				delete pixels;
				pixels = nullptr;
#endif // 0

				
			}

我们可以实现的功能效果: 在屏幕上绘制任意的闭合多边形,并拾取内部的图元