我是Windows API的新手。使用 Winapi 教程中提供的一些 Windows 示例代码：
Graphics.DrawImage（Image*， const Rect） 方法
我想打开一个.jpg图像并将其绘制到我创建的新窗口中。 问题是我不确定如何在现有窗口中使用 VOID Example_DrawImage9(HDC hdc) 方法。我的第一直觉是在回调过程中case WM_PAINT内部调用它，并从那里使用hdc，但图像不显示。我如何知道正确的供应hdc？我应该在哪里调用该方法？
#include <windows.h>
#include "stdafx.h"
#include <objidl.h>
#include <gdiplus.h>
using namespace Gdiplus;
#pragma comment (lib,"Gdiplus.lib")
//*************************************************** added for gdiplus
HWND hEdit;
//************************************************how do I use this method with the window I have created below?
VOID Example_DrawImage9(HDC hdc){
Graphics graphics(hdc); // Create an Image object.
Image image(L"C:/Users/Me/Desktop/fuzz.jpg"); // Create a Pen object.
Pen pen(Color(255, 255, 0, 0), 2); // Draw the original source image.
graphics.DrawImage(&image, 10, 10); // Create a Rect object that specifies the destination of the image.
Rect destRect(200, 50, 150, 75); // Draw the rectangle that bounds the image.
graphics.DrawRectangle(&pen, destRect); // Draw the image.
graphics.DrawImage(&image, destRect);
}
//*********************************************************************************************
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
const wchar_t CLASS_NAME[] = L"Sample Window Class";
WNDCLASS wc = {};
wc.lpfnWndProc = WindowProc; //attach this callback procedure
wc.hInstance = hInstance; //handle to application instance
wc.lpszClassName = CLASS_NAME;
RegisterClass(&wc); //register wc
// Create the window.
HWND hwnd = CreateWindowEx(
0, // Optional window styles.
CLASS_NAME, // Window class
L"Learn to Program Windows", // Window text
WS_OVERLAPPEDWINDOW, // Window style
// Size and position
CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
NULL, // Parent window
NULL, // Menu
hInstance, // Instance handle
NULL // Additional application data
);
if (hwnd == NULL){
return 0;
}
ShowWindow(hwnd, nCmdShow);
MSG msg = {};
while (GetMessage(&msg, NULL, 0, 0)){
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return 0;
}
//callback procedure for this window, takes in all the window details
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam){
switch (uMsg){
case WM_DESTROY:
PostQuitMessage(0);
return 0;
case WM_PAINT:{
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hwnd, &ps);
//***************************************************************
//do we call DrawImage here? what do we need to pass as hdc?
//Example_DrawImage9(HDC hdc);//?????????????
//***************************************************************
FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 1));
EndPaint(hwnd, &ps);
}
return 0;
}
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
你走在正确的轨道上。 使用BeginPaint()提供的HDC。 并且不要忘记在使用之前初始化GDI+。
#include <windows.h>
#include "stdafx.h"
#include <objidl.h>
#include <gdiplus.h>
using namespace Gdiplus;
#pragma comment (lib, "Gdiplus.lib")
void Example_DrawImage9(HDC hdc)
{
Graphics graphics(hdc);
// Create an Image object.
Image image(L"C:/Users/Me/Desktop/fuzz.jpg");
// Create a Pen object.
Pen pen(Color(255, 255, 0, 0), 2);
// Draw the original source image.
graphics.DrawImage(&image, 10, 10);
// Create a Rect object that specifies the destination of the image.
Rect destRect(200, 50, 150, 75);
// Draw the rectangle that bounds the image.
graphics.DrawRectangle(&pen, destRect);
// Draw the image.
graphics.DrawImage(&image, destRect);
}
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
ULONG_PTR token;
GdiplusStartupInput input = {0};
input.GdiplusVersion = 1;
GdiplusStartup(&token, &input, NULL);
const wchar_t CLASS_NAME[] = L"Sample Window Class";
WNDCLASS wc = {};
wc.lpfnWndProc = &WindowProc; //attach this callback procedure
wc.hInstance = hInstance; //handle to application instance
wc.lpszClassName = CLASS_NAME;
RegisterClass(&wc); //register wc
// Create the window.
HWND hwnd = CreateWindowEx(
0, // Optional window styles.
CLASS_NAME, // Window class
L"Learn to Program Windows", // Window text
WS_OVERLAPPEDWINDOW, // Window style
// Size and position
CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
NULL, // Parent window
NULL, // Menu
hInstance, // Instance handle
NULL // Additional application data
);
if (hwnd != NULL)
{
ShowWindow(hwnd, nCmdShow);
MSG msg;
while (GetMessage(&msg, NULL, 0, 0) > 0)
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
GdiplusShutdown(token);
return 0;
}
//callback procedure for this window, takes in all the window details
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg)
{
case WM_DESTROY:
PostQuitMessage(0);
return 0;
case WM_PAINT:
{
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hwnd, &ps);
FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 1));
Example_DrawImage9(hdc);
EndPaint(hwnd, &ps);
return 0;
}
}
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
您必须初始化 GDI+，然后在退出之前将其关闭。
int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
Gdiplus::GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
Gdiplus::GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
//...
Gdiplus::GdiplusShutdown(gdiplusToken);
return 0;
}
graphics.DrawImage(&image, 10, 10);足以描绘图像。绘制图像后，不要在其上绘制任何其他内容。
您可以在 WM_PAINT 中使用Example_DrawImage9(hdc)。在绘制图像之前使用FillRect。