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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。
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