Visual C++游戏编程基础之透明半透明效果

一、基本思路

1.半透明的原理

一张位图由许多像素组成，而每一像素包含R、G、B三原色，三原色的值决定了像素的色彩，要实现半透明效果，需要把前景图和背景图彼此对应的像素颜色按某一比例进行调配，称为 ‘不透明度’，直接贴图，则前景图不透明度为100%,背景图为0%；

公式：半透明图色彩=前景图色彩 * 不透明度 + 背景图色彩 * (1-不透明度)

2.半透明操作步骤

(1)取得位图结构，需要使用GetObject函数，介绍如下：

函数原型：int GetObject(HGDIOBJ hgdiobj, int cbBuffer, LPVOID lpvObject)；

函数功能：表示获取位图的信息

参数一：要获取的位图句柄

参数二：指定将要写到缓冲区的信息的字节数目，在这里是位图类型的字节数

参数三：在这里是指向位图结构变量的地址，该变量当作缓冲区

关于位图结构BITMAP介绍如下：

(2)建立暂存数组，目的是为了存储位图中所有像素的颜色值

unsigned char * px1 = new unsigned char [bm1.bmHeight * bm1.bmWidthBytes];

其中数组的大小即为整个位图所有像素占的字节数，若一个像素24bits，则占3个字节，也就是3个数组元素

(3)取得位图中所有的颜色值，并存储到暂存数组中，函数介绍如下：

函数原型：LONG GetBitmapBits(HBITMAP hbmp, LONG cbBuffer, LPVOID lpvBits)；

函数功能：把位图的色彩值存储到暂存数组中

参数一：位图句柄

参数二：要取得的字节数

参数三：指向暂存数组

(4)合成像素颜色值，这里介绍基本思想：

假设每个像素24bit，则每个像素占3字节，关于背景图，首先要取得整张图像素各原色值所在的索引值，即：

 for(y=ystart;y<yend;y++)  {for(x=xstart;x<xend;x++) //对背景图贴图部分做颜色处理{rgb_b = y * bm1.bmWidthBytes + x * PxBytes ;//像素各原色值存储的元素索引值px1[rgb_b] = px1[rgb_b] * 0.7;               //PxBytes为每个像素所占的字节数px1[rgb_b+1] = px1[rgb_b+1] * 0.7;           //bmWidthBytes为每一列像素占的字节数px1[rgb_b+2] = px1[rgb_b+2] * 0.7;  }}

举个简单的例子，假设从(xstart,ystary)~(xend,yend) 为 (0,0)~(1,1)，则有如下情况：

[0][1][2] [3][4][5]

[6][7][8] [9][10][11]

注释：每个像素占3个字节；每一列像素占6字节，书里都把行称为列，也不知道为啥

同理：处理前景图时，直接进行颜色合成：前景图30%的不透明度+背景图70%的不透明度，存放到px2

for(y=0;y<(bm2.bmHeight); y++)     {for(x=0;x<bm2.bmWidth; x++) {rgb_b = y * bm2.bmWidthBytes + x * PxBytes ;i = (ystart+y) * bm1.bmWidthBytes + (xstart+x) * PxBytes;px2[rgb_b]   = px2[rgb_b]  *0.3 + px1[i];  //半透明色彩合成px2[rgb_b+1] = px2[rgb_b+1] *0.3 + px1[i+1];  px2[rgb_b+2] = px2[rgb_b+2] *0.3 + px1[i+2];}}

(5)重设位图颜色，根据暂存数组中的内容重设位图颜色

函数原型：LONG SetBitmapBits(HBITMAP hmbp, DWORD cBytes, CONST VOID (lpBits));

函数功能：重设位图颜色

参数一：要设置的位图句柄

参数二：暂存数组的字节数

参数三：指向暂存数组

二、结合前面所学的实现透明半透明效果，代码如下：


#include "stdafx.h"
#include <stdio.h>HINSTANCE hInst;
HBITMAP bg,girl;
HDC     mdc;const int xstart = 222;
const int ystart = 50;ATOM             MyRegisterClass(HINSTANCE hInstance);
BOOL                InitInstance(HINSTANCE, int);
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);
void                MyPaint(HDC hdc);int APIENTRY WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR     lpCmdLine,int       nCmdShow)
{MSG msg;MyRegisterClass(hInstance);if (!InitInstance (hInstance, nCmdShow)) {return FALSE;}while (GetMessage(&msg, NULL, 0, 0)) {TranslateMessage(&msg);DispatchMessage(&msg);}return msg.wParam;
}ATOM MyRegisterClass(HINSTANCE hInstance)
{WNDCLASSEX wcex;wcex.cbSize = sizeof(WNDCLASSEX); wcex.style          = CS_HREDRAW | CS_VREDRAW;wcex.lpfnWndProc = (WNDPROC)WndProc;wcex.cbClsExtra     = 0;wcex.cbWndExtra        = 0;wcex.hInstance     = hInstance;wcex.hIcon         = NULL;wcex.hCursor        = NULL;wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);wcex.hbrBackground   = (HBRUSH)(COLOR_WINDOW+1);wcex.lpszMenuName  = NULL;wcex.lpszClassName  = "canvas";wcex.hIconSm      = NULL;return RegisterClassEx(&wcex);
}BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{HWND hWnd;HDC hdc,bufdc;HBITMAP bmp;BITMAP bm1,bm2;hInst = hInstance;hWnd = CreateWindow("canvas", "绘图窗口" , WS_OVERLAPPEDWINDOW,CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);if (!hWnd){return FALSE;}MoveWindow(hWnd,10,10,600,445,true);ShowWindow(hWnd, nCmdShow);UpdateWindow(hWnd);bg = (HBITMAP)LoadImage(NULL,"bg.bmp",IMAGE_BITMAP,600,400,LR_LOADFROMFILE); //背景图句柄bmp = (HBITMAP)LoadImage(NULL,"girlmask.bmp",IMAGE_BITMAP,766,345,LR_LOADFROMFILE);//前景图句柄GetObject(bg,sizeof(BITMAP),&bm1);     //get the message of image to bm1if(bm1.bmBitsPixel != 32 && bm1.bmBitsPixel != 24) //bit of pixe     l{MessageBox(NULL,"此程序只能在32 bit 或 24 bit 显示模式中运行","警告",0);return FALSE;}hdc = GetDC(hWnd);mdc = CreateCompatibleDC(hdc);//建立与窗口DC兼容的内存DC "mdc"bufdc = CreateCompatibleDC(hdc);//建立与窗口DC兼容的内存DC "bufdc",选择前景图或背景图，贴到mdc作透明处理girl = CreateCompatibleBitmap(hdc,383,345);//建立一个与窗口相兼容的空位图"girl",298*329像素,处理后就是要贴到窗口的透明半透明图案SelectObject(mdc,girl);//girl 存到 mdc，在mdc上进行透明处理SelectObject(bufdc,bg);//bg replace bufdc,背景图bg存入bufdcBitBlt(mdc,0,0,383,345,bufdc,xstart,ystart,SRCCOPY);//将透明区域的背景图贴到mdc中SelectObject(bufdc,bmp);//将包含屏蔽图的前景图存入bufdcBitBlt(mdc,0,0,383,345,bufdc,383,0,SRCAND);//屏蔽图在整张图中，左上角坐标(298,0),屏蔽图与背景图and运算BitBlt(mdc,0,0,383,345,bufdc,0,0,SRCPAINT);//前景图与背景图or运算，得到透明后的前景图，接下来进行半透明处理unsigned char *px1,*px2;px1 = new unsigned char [bm1.bmHeight * bm1.bmWidthBytes];GetBitmapBits(bg,bm1.bmHeight * bm1.bmWidthBytes,px1);//px1储存位图颜色值GetObject(girl,sizeof(BITMAP),&bm2);//bme得到girl的全部信息px2 = new unsigned char [bm2.bmHeight * bm2.bmWidthBytes];GetBitmapBits(girl,bm2.bmHeight * bm2.bmWidthBytes,px2);//px2储存位图bm2的颜色值int x,y,xend,yend;int i;int rgb_b;int PxBytes = bm1.bmBitsPixel / 8 ;xend = xstart + 383;yend = ystart + 345;for(y=ystart;y<yend;y++)     {for(x=xstart;x<xend;x++) {rgb_b = y * bm1.bmWidthBytes + x * PxBytes ;px1[rgb_b] = px1[rgb_b] * 0.7;      px1[rgb_b+1] = px1[rgb_b+1] * 0.7;       px1[rgb_b+2] = px1[rgb_b+2] * 0.7;       }}for(y=0;y<(bm2.bmHeight); y++)  {for(x=0;x<bm2.bmWidth; x++) {rgb_b = y * bm2.bmWidthBytes + x * PxBytes ;i = (ystart+y) * bm1.bmWidthBytes + (xstart+x) * PxBytes;px2[rgb_b]    = px2[rgb_b] *0.3 + px1[i];  px2[rgb_b+1] = px2[rgb_b+1] *0.3 + px1[i+1];   px2[rgb_b+2] = px2[rgb_b+2] *0.3 + px1[i+2];   }}SetBitmapBits(girl,bm2.bmHeight*bm2.bmWidthBytes,px2);MyPaint(hdc);ReleaseDC(hWnd,hdc);DeleteDC(bufdc);DeleteObject(bmp);delete [] px1;delete [] px2;return TRUE;
}void MyPaint(HDC hdc)
{SelectObject(mdc,bg);//bg replace mdc,bg存入到mdc中BitBlt(hdc,0,0,600,400,mdc,0,0,SRCCOPY);//将mdc贴到hdcSelectObject(mdc,girl);BitBlt(hdc,xstart,ystart,383,345,mdc,0,0,SRCCOPY);
}LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{PAINTSTRUCT ps;HDC hdc;switch (message){case WM_PAINT:                     hdc = BeginPaint(hWnd, &ps);MyPaint(hdc);EndPaint(hWnd, &ps);break;case WM_DESTROY:                DeleteDC(mdc);DeleteObject(bg);DeleteObject(girl);PostQuitMessage(0);break;default:                     return DefWindowProc(hWnd, message, wParam, lParam);}return 0;
}

四、效果