Direct2D 几何图形绘制基础

之前说过，D2D主要为了绘制有三种类型的数据：几何图形，图片，文字。这几种对象也叫做资源，资源就是要D2D流水线中要被加工的对象。

几何图形包括：

简单几何图形

直线，DrawLine，由起点和终点构成，点用结构体：D2D1_POINT_2F描述。
矩形，ID2D1RectangleGeometry，DrawRectangle，由距四条边的距离表示，用结构体：D2D1_RECT_F描述。
圆角矩形，ID2D1RoundedRectangleGeometry ，DrawRoundedRectangle，同矩形，用结构体：D2D1_ROUNDED_RECT描述，另外还要加入圆角参数。
椭圆，包括圆，ID2D1EllipseGeometry ，DrawEllipse，用结构体：D2D1_ELLIPSE
描述。

路径，ID2D1PathGeometry
组合图形，

几何图形组合，ID2D1GeometryGroup
变幻几何图形，ID2D1TransformedGeometry

准备绘制：

在开始绘制之前，至少要准备好3样东西：

D2D工厂对象，ID2D1Factory接口。用于创建绘制目标，用方法CreateHwndRenderTarget。

渲染窗口，ID2D1HwndRenderTarget接口。如果是Win32程序就是默认的HWND窗口，如果是商店应用则是一个绘制表面的控件。

渲染窗口同时还负责着绘制几何图形，文字和图片。

画刷，ID2D1SolidColorBrush接口。绘制几何图形时用于指定图形的样式。
绘制区域，如果是win32程序还需要指定渲染窗口中要绘制的区域。

首先要引入头文件和命名空间：

#include "windows.h"
#include "D2D1.h"

using namespace D2D1;

别忘了加要链接的Lib，要input的lib如下：
d2d1.lib;
dxgi.lib;
dwrite.lib;
dxguid.lib;

windowscodecs.lib;

声明以上4个对象的代码如下：

// Direct2D factory
	ID2D1Factory* pD2DFactory; 
	// Render target
	ID2D1HwndRenderTarget* pRenderTarget;
	// A black brush, reflect the line color
	ID2D1SolidColorBrush* pBlackBrush; 
	// Render area
	RECT rc ;

初始化这些值的代码如下：

//create d2d factory
	hr =  D2D1CreateFactory(D2D1_FACTORY_TYPE_SINGLE_THREADED, &pD2DFactory) ;
	//create render target (hwnd window)
	GetClientRect(hWnd, &rc);
	hr = pD2DFactory->CreateHwndRenderTarget( RenderTargetProperties(), HwndRenderTargetProperties(hWnd, SizeU(rc.right - rc.left, rc.bottom - rc.top)), &pRenderTarget);
	//create brush
	hr = pRenderTarget->CreateSolidColorBrush(ColorF(ColorF::Blue), &pBlackBrush);

然后就可以开始绘制了。笔者使用的程序是win32应用程序，绘制的代码都必须写在WndProc回调函数的case WM_PAINT:之后，并且要将所有绘制代码都包含在pRenderTarget->BeginDraw();和pRenderTarget->EndDraw();之间。例如：

pRenderTarget->BeginDraw();

	//clear screen
	pRenderTarget->Clear(D2D1::ColorF(D2D1::ColorF::White));

	//draw line with 2 points
	D2D1_POINT_2F ptStart = Point2F(0,0);
	D2D1_POINT_2F ptEnd = Point2F(100,100);
	pRenderTarget->DrawLine(ptStart,ptEnd,pBlackBrush);
	
	//draw rectangle
	D2D1_RECT_F rect  = RectF(rc.left + 100.0f, rc.top + 100.0f, rc.right - 100.0f, rc.bottom - 100.0f);
	pRenderTarget->DrawRectangle(rect, pBlackBrush);

	//draw round rect
	D2D1_ROUNDED_RECT roundrect  = RoundedRect(RectF(rc.left + 100.0f, rc.top + 100.0f, rc.right - 100.0f, rc.bottom - 100.0f), 30.0f, 50.0f);
	pRenderTarget->DrawRoundedRectangle(roundrect, pBlackBrush, 1.0f);

	pRenderTarget->EndDraw();

WM_PAINT是在窗口需要重绘时由系统调用的，所以我们不用主动地去调用它，它们不断地刷新的。

当然了，把代码都积压在WM_PAINT之后也太SB了，最好自己封装一个类，如下：
头文件如下：

#pragma once

#include "stdafx.h"
#include "windows.h"
#include "D2D1.h"

using namespace D2D1;

class D2DRender
{
public:
	D2DRender(void);
	~D2DRender(void);
	
	HRESULT CreateDeviceIndependentResources();
	HRESULT CreateDeviceResources(HWND hWnd);
	void OnRender();
	void DiscardDeviceResources();
	void OnResize(UINT width, UINT height);

private:
// Direct2D factory
	ID2D1Factory* pD2DFactory; 
	// Render target
	ID2D1HwndRenderTarget* pRenderTarget;
	// A black brush, reflect the line color
	ID2D1SolidColorBrush* pBlackBrush; 
	// Render area
	RECT rc ;
	//result
	HRESULT hr;
};

实现如下：

#include "stdafx.h"
#include "D2DRender.h"

D2DRender::D2DRender()
{
	// Direct2D factory
	pD2DFactory = NULL; 
	// Render target
	pRenderTarget = NULL;
	// A black brush, reflect the line color
	pBlackBrush = NULL; 	
}

D2DRender::~D2DRender()
{
	pD2DFactory->Release();
	pRenderTarget->Release();
	pBlackBrush->Release();

}

void D2DRender::DiscardDeviceResources()
{
	pD2DFactory->Release();
	pRenderTarget->Release();
	pBlackBrush->Release();
}

void D2DRender::OnResize(UINT width, UINT height)
{
	if(pRenderTarget)
	{
		pRenderTarget->Resize(SizeU(width,height));
	}
}

HRESULT D2DRender::CreateDeviceIndependentResources()
{
	//create d2d factory
	hr =  D2D1CreateFactory(D2D1_FACTORY_TYPE_SINGLE_THREADED, &pD2DFactory) ;

	return hr;
}

HRESULT D2DRender::CreateDeviceResources(HWND hWnd)
{
	//create render target (hwnd window)
	GetClientRect(hWnd, &rc);
	hr = pD2DFactory->CreateHwndRenderTarget( RenderTargetProperties(), HwndRenderTargetProperties(hWnd, SizeU(rc.right - rc.left, rc.bottom - rc.top)), &pRenderTarget);

	//create brush
	hr = pRenderTarget->CreateSolidColorBrush(ColorF(ColorF::Blue), &pBlackBrush);

	return hr;
}

void D2DRender::OnRender()
{
pRenderTarget->BeginDraw();

	//clear screen
	pRenderTarget->Clear(D2D1::ColorF(D2D1::ColorF::White));

	//draw line with 2 points
	D2D1_POINT_2F ptStart = Point2F(0,0);
	D2D1_POINT_2F ptEnd = Point2F(100,100);
	pRenderTarget->DrawLine(ptStart,ptEnd,pBlackBrush);
	
	//draw rectangle
	D2D1_RECT_F rect  = RectF(rc.left + 100.0f, rc.top + 100.0f, rc.right - 100.0f, rc.bottom - 100.0f);
	pRenderTarget->DrawRectangle(rect, pBlackBrush);

	//draw round rect
	D2D1_ROUNDED_RECT roundrect  = RoundedRect(RectF(rc.left + 100.0f, rc.top + 100.0f, rc.right - 100.0f, rc.bottom - 100.0f), 30.0f, 50.0f);
	pRenderTarget->DrawRoundedRectangle(roundrect, pBlackBrush, 1.0f);

	pRenderTarget->EndDraw();
}

然后在WM_PANIT里调用，默认生成的gdi绘制用到的hdc相关代码可以删掉。

case WM_PAINT:
		//hdc = BeginPaint(hWnd, &ps);
		D2DRender pRender;
		pRender.CreateDeviceIndependentResources();
		pRender.CreateDeviceResources(hWnd);
		pRender.OnRender();
		//EndPaint(hWnd, &ps);
		break;

还是比较简单。