How to use DrawLine in C++ (DirectX Graphics) - directx

Question

// Draw a grid background.
int width = static_cast<int>(rtSize.width);
int height = static_cast<int>(rtSize.height);
for (int x = 0; x < width; x += 10)
{
m_pRenderTarget->DrawLine(
D2D1::Point2F(static_cast<FLOAT>(x), 0.0f),
D2D1::Point2F(static_cast<FLOAT>(x), rtSize.height),
m_pLightSlateGrayBrush,
0.5f
);
}
This is the sample in the documentation. I've included "D2d1.h", I just don't know how to create a "m_pRenderTarget". I'm writing a Kinect project, I want to draw a line on the image. I'm really new, please help me.

Answer 1

Have you see this page?
Create an ID2D1HwndRenderTarget
The quick start tutorial has a detail steps of how to use Direct2D.
You can also download the Windows SDK, the samples contains Direct2D demo which has the full steps of how to create Direct2D render target
I have write a program to draw a rectangle, with a little change, it can draw a line, just for your reference
#include <windows.h>
#include <D2D1.h>
#define SAFE_RELEASE(P) if(P){P->Release() ; P = NULL ;}
ID2D1Factory* g_pD2DFactory = NULL; // Direct2D factory
ID2D1HwndRenderTarget* g_pRenderTarget = NULL; // Render target
ID2D1SolidColorBrush* g_pBlackBrush = NULL; // A black brush, reflect the line color
VOID CreateD2DResource(HWND hWnd)
{
if (!g_pRenderTarget)
{
HRESULT hr ;
hr = D2D1CreateFactory(D2D1_FACTORY_TYPE_SINGLE_THREADED, &g_pD2DFactory) ;
if (FAILED(hr))
{
MessageBox(hWnd, "Create D2D factory failed!", "Error", 0) ;
return ;
}
// Obtain the size of the drawing area
RECT rc ;
GetClientRect(hWnd, &rc) ;
// Create a Direct2D render target
hr = g_pD2DFactory->CreateHwndRenderTarget(
D2D1::RenderTargetProperties(),
D2D1::HwndRenderTargetProperties(
hWnd,
D2D1::SizeU(rc.right - rc.left,rc.bottom - rc.top)
),
&g_pRenderTarget
) ;
if (FAILED(hr))
{
MessageBox(hWnd, "Create render target failed!", "Error", 0) ;
return ;
}
// Create a brush
hr = g_pRenderTarget->CreateSolidColorBrush(
D2D1::ColorF(D2D1::ColorF::Black),
&g_pBlackBrush
) ;
if (FAILED(hr))
{
MessageBox(hWnd, "Create brush failed!", "Error", 0) ;
return ;
}
}
}
VOID DrawLine(HWND hwnd)
{
CreateD2DResource(hwnd) ;
g_pRenderTarget->BeginDraw() ;
// Clear background color to White
g_pRenderTarget->Clear(D2D1::ColorF(D2D1::ColorF::White));
// Draw Rectangle
g_pRenderTarget->DrawLine(
D2D1::Point2F(100.0f, 100.0f),
D2D1::Point2F(500.0f, 500.0f),
g_pBlackBrush
);
HRESULT hr = g_pRenderTarget->EndDraw() ;
if (FAILED(hr))
{
MessageBox(NULL, "Draw failed!", "Error", 0) ;
return ;
}
}
VOID Cleanup()
{
SAFE_RELEASE(g_pRenderTarget) ;
SAFE_RELEASE(g_pBlackBrush) ;
SAFE_RELEASE(g_pD2DFactory) ;
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_PAINT:
DrawLine(hwnd) ;
return 0 ;
case WM_KEYDOWN:
{
switch( wParam )
{
case VK_ESCAPE:
SendMessage( hwnd, WM_CLOSE, 0, 0 );
break ;
default:
break ;
}
}
break ;
case WM_DESTROY:
Cleanup();
PostQuitMessage( 0 );
return 0;
}
return DefWindowProc (hwnd, message, wParam, lParam) ;
}
int WINAPI WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow )
{
WNDCLASSEX winClass ;
winClass.lpszClassName = "Direct2D";
winClass.cbSize = sizeof(WNDCLASSEX);
winClass.style = CS_HREDRAW | CS_VREDRAW;
winClass.lpfnWndProc = WndProc;
winClass.hInstance = hInstance;
winClass.hIcon = NULL ;
winClass.hIconSm = NULL ;
winClass.hCursor = LoadCursor(NULL, IDC_ARROW);
winClass.hbrBackground = NULL ;
winClass.lpszMenuName = NULL;
winClass.cbClsExtra = 0;
winClass.cbWndExtra = 0;
if (!RegisterClassEx (&winClass))
{
MessageBox ( NULL, TEXT( "This program requires Windows NT!" ), "error", MB_ICONERROR) ;
return 0 ;
}
HWND hwnd = CreateWindowEx(NULL,
"Direct2D", // window class name
"Draw Rectangle", // window caption
WS_OVERLAPPEDWINDOW, // window style
CW_USEDEFAULT, // initial x position
CW_USEDEFAULT, // initial y position
600, // initial x size
600, // initial y size
NULL, // parent window handle
NULL, // window menu handle
hInstance, // program instance handle
NULL) ; // creation parameters
ShowWindow (hwnd, iCmdShow) ;
UpdateWindow (hwnd) ;
MSG msg ;
ZeroMemory(&msg, sizeof(msg)) ;
while (GetMessage (&msg, NULL, 0, 0))
{
TranslateMessage (&msg) ;
DispatchMessage (&msg) ;
}
return msg.wParam ;
}