OpenGL学习笔记：截图生成图片

GLuint CaptureScreen(int width, int height, std::function<void()> foo)
{
	foo();
	unsigned char * screenPixel = new unsigned char[width*height*3];
	glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, screenPixel);
	GLuint texture;
	//generate an opengl texture
	glGenTextures(1, &texture);
	glBindTexture(GL_TEXTURE_2D, texture);
	//operation on current texture
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, screenPixel);
	glBindTexture(GL_TEXTURE_2D, 0);
	delete screenPixel;
	return texture;
}

Texture*screenTexture = new Texture;
screenTexture->mTextureID = CaptureScreen(viewportWidth, viewportHeight, []()->void 
{
	RenderOneFrame(0.0f); // 这里是真实的draw,也是CaptureScreen的参数foo
});
sprite.SetTexture(screenTexture);

SaveScreenPixelToFile(viewportWidth, viewportHeight, []()->void
{
	RenderOneFrame(0.0f);
}, "screenshot.bmp");

//==============================================================

void SaveScreenPixelToFile(int width, int height, std::function<void()> foo, const char*filePath)
{
	foo();
	unsigned char * screenPixel = new unsigned char[width*height * 3];
	glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, screenPixel);

	FILE*pFile = fopen(filePath, "wb");
	if (pFile)
	{
		BITMAPFILEHEADER bfh;
		memset(&bfh, 0, sizeof(BITMAPFILEHEADER));
		bfh.bfType = 0x4D42; //0x4D42="BM"，是Bitmap文件的标志。
		bfh.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + width*height * 3;
		bfh.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
		fwrite(&bfh, sizeof(BITMAPFILEHEADER), 1, pFile);

		BITMAPINFOHEADER bih;
		memset(&bih, 0, sizeof(BITMAPINFOHEADER));
		bih.biWidth = width;
		bih.biHeight = height;
		bih.biBitCount = 24;
		bih.biSize = sizeof(BITMAPINFOHEADER);
		fwrite(&bih,sizeof(BITMAPINFOHEADER),1,pFile);

		//rgb -> bgr
		for (int i = 0; i < width*height * 3; i += 3)
		{
			unsigned char temp = screenPixel[i];
			screenPixel[i] = screenPixel[i + 2];
			screenPixel[i + 2] = temp;
		}
		fwrite(screenPixel, 1, width*height * 3, pFile);
		fclose(pFile);
	}
}

glEnable(GL_SCISSOR_TEST);
glScissor(0, 0, viewportWidth/2, viewportHeight);