Iczelion's Win32 Assembly Tutorial 25: Simple Bitmap

Tutorial 25: Simple Bitmap

In this tutorial, we will learn how to use bitmap in our program. To be exact, we will learn how to display a bitmap in the client area of our window.

Download the example.

Theory

Bitmaps can be thought of as pictures stored in computer. There are many picture formats used with computers but Windows only natively supports Windows Bitmap Graphics files (.bmp). The bitmaps I'll refer to in this tutorial are Windows bitmap graphics files. The easiest way to use a bitmap is to use it as a resource. There are two ways to do that. You can include the bitmap in the resource definition file (.rc) as follows:

#define IDB_MYBITMAP 100
IDB_MYBITMAP bitmap  "c:\project\example.bmp"

This method uses a constant to represent the bitmap. The first line just creates a constant named IDB_MYBITMAP which has the value of 100. We will use this label to refer to the bitmap in the program. The next line declares a bitmap resource. It tells the resource compiler where to find the actual bmp file.

The other method uses a name to represent the bitmap as follows: MyBitMap bitmap "c:\project\example.bmp"

This method requires that you refer to the bitmap in your program by the string "MyBitMap" instead of a value.

Either method works fine as long as you know which method you're using.

Now that we put the bitmap in the resource file, we can go on with the steps in displaying it in the client area of our window.

call LoadBitmap to get the bitmap handle. LoadBitmap has the following definition: LoadBitmap PROTO hInstance:HINSTANCE, lpBitmapName:LPSTR

This function returns a bitmap handle. hInstance is the instance handle of our program. lpBitmapName is a pointer to the string that is the name of the bitmap (incase you use the second method to refer to the bitmap). If you use a constant to refer to the bitmap (like IDB_MYBITMAP), you can put its value here. (In the example above it would be 100). A short example is in order:

First Method:
.386 .model flat, stdcall ................ .const IDB_MYBITMAP equ 100 ............... .data? hInstance dd ? .............. .code ............. invoke GetModuleHandle,NULL mov hInstance,eax ............ invoke LoadBitmap,hInstance,IDB_MYBITMAP ...........
Second Method:
.386 .model flat, stdcall ................ .data BitmapName db "MyBitMap",0 ............... .data? hInstance dd ? .............. .code ............. invoke GetModuleHandle,NULL mov hInstance,eax ............ invoke LoadBitmap,hInstance,ADDR BitmapName ...........
1. Obtain a handle to device context (DC). You can obtain this handle by calling BeginPaint in response to WM_PAINT message or by calling GetDC anywhere.
2. Create a memory device context which has the same attribute as the device context we just obtained. The idea here is to create a kind of "hidden" drawing surface which we can draw the bitmap on. When we are finished with the operation, we just copy the content of the hidden drawing surface to the actual device context in one function call. It's an example of double-buffer technique used for fast display of pictures on the screen. You can create this "hidden" drawing surface by calling CreateCompatibleDC.
CreateCompatibleDC PROTO hdc:HDC
- If this function succeeds, it returns the handle of the memory device context in eax. hdc is the handle to the device context that you want the memory DC to be compatible with.
- Now that you got a hidden drawing surface, you can draw on it by selecting the bitmap into it. This is done by calling SelectObject with the handle to the memory DC as the first parameter and the bitmap handle as the second parameter. SelectObject has the following definition:
SelectObject PROTO hdc:HDC, hGdiObject:DWORD
- The bitmap is drawn on the memory device context now. All we need to do here is to copy it to the actual display device, namely the true device context. There are several functions that can perform this operation such as BitBlt and StretchBlt. BitBlt just copies the content of one DC to another so it's fast while StretchBlt can stretch or compress the bitmap to fit the output area. We will use BitBlt here for simplicity. BitBlt has the following definition:
BitBlt PROTO hdcDest:DWORD, nxDest:DWORD, nyDest:DWORD, \ nWidth:DWORD, nHeight:DWORD, \ hdcSrc:DWORD, nxSrc:DWORD, \ nySrc:DWORD, dwROP:DWORD
- hdcdest is the handle of the device context that serves as the destination of bitmap transfer operation.
- nxDest,
  nyDest are the coordinate of the upper left corner of the output area.
- nWidth,
  nHeight are the width and height of the output area.
- hdcSrc is the handle of the device context that serves as the source of bitmap transfer operation.
- nxSrc,
  nySrc are the coordinate of the upper left corner of the source rectangle.
- dwROP is the raster-operation code (hence the acronym ROP) that governs how to combine the color data of the bitmap to the existing color data on the output area to achieve the final result. Most of the time, you only want to overwrite the existing color data with the new one.

When you're done with the bitmap, delete it with DeleteObject API call.

That's it! To recapitulate, you need to put the bitmap into the resource scipt. Then load it from the resource with LoadBitmap. You'll get the bitmap handle. Next you obtain the handle to the device context of the area you want to paint the bitmap on. Then you create a memory device context that is compatible with the device context you just obtained. Select the bitmap into the memory DC then copy the content of the memory DC to the real DC.

Example Code:

.386
.model FLAT,STDCALL
OPTION casemap:none

include    \masm32\include\windows.inc
include    \masm32\include\user32.inc
include    \masm32\include\kernel32.inc
include    \masm32\include\gdi32.inc
includelib \masm32\lib\user32.lib
includelib \masm32\lib\kernel32.lib
includelib \masm32\lib\gdi32.lib

WinMain PROTO :DWORD,:DWORD,:DWORD,:DWORD

IDB_MAIN  equ 1

.data
ClassName db "SimpleWin32ASMBitmapClass",0
AppName   db "Win32ASM Simple Bitmap Example",0

.data? 
hInstance   HINSTANCE ? 
CommandLine LPSTR     ? 
hBitmap     dd        ? 

.code
start:
        invoke GetModuleHandle, NULL
        mov    hInstance,eax
        invoke GetCommandLine
        mov    CommandLine,eax
        invoke WinMain, hInstance,NULL,CommandLine, SW_SHOWDEFAULT
        invoke ExitProcess,eax
WinMain PROC hInst:HINSTANCE,hPrevInst:HINSTANCE,CmdLine:LPSTR,
             CmdShow:DWORD
LOCAL wc:WNDCLASSEX
LOCAL msg:MSG
LOCAL hwnd:HWND
        mov    wc.cbSize,SIZEOF WNDCLASSEX
        mov    wc.style, CS_HREDRAW or CS_VREDRAW
        mov    wc.lpfnWndProc, OFFSET WndProc
        mov    wc.cbClsExtra,NULL
        mov    wc.cbWndExtra,NULL
        push   hInstance
        pop    wc.hInstance
        mov    wc.hbrBackground,COLOR_WINDOW+1
        mov    wc.lpszMenuName,NULL
        mov    wc.lpszClassName,OFFSET ClassName
        invoke LoadIcon,NULL,IDI_APPLICATION
        mov    wc.hIcon,eax
        mov    wc.hIconSm,eax
        invoke LoadCursor,NULL,IDC_ARROW
        mov    wc.hCursor,eax
        invoke RegisterClassEx, ADDR wc
        invoke CreateWindowEx,NULL,ADDR ClassName,ADDR AppName,\
                              WS_OVERLAPPEDWINDOW,             \
                              CW_USEDEFAULT,CW_USEDEFAULT,     \
                              CW_USEDEFAULT,CW_USEDEFAULT,     \
                              NULL,NULL,hInst,NULL
        mov    hwnd,eax
        invoke ShowWindow, hwnd,SW_SHOWNORMAL
        invoke UpdateWindow, hwnd
.WHILE TRUE
        invoke GetMessage, ADDR msg,NULL,0,0
.BREAK .IF (!eax)
        invoke TranslateMessage, ADDR msg
        invoke DispatchMessage, ADDR msg
.ENDW
        mov    eax,msg.wParam
        ret
WinMain ENDP

WndProc PROC hWnd:HWND, uMsg:UINT, wParam:WPARAM, lParam:LPARAM
LOCAL ps:PAINTSTRUCT
LOCAL hdc:HDC
LOCAL hMemDC:HDC
LOCAL rect:RECT
.IF uMsg==WM_CREATE
        invoke LoadBitmap,hInstance,IDB_MAIN
        mov    hBitmap,eax
.ELSEIF uMsg==WM_PAINT
        invoke BeginPaint,hWnd,ADDR ps
        mov    hdc,eax
        invoke CreateCompatibleDC,hdc>
        mov    hMemDC,eax
        invoke SelectObject,hMemDC,hBitmap
        invoke GetClientRect,hWnd,ADDR rect
        invoke BitBlt,hdc,0,0,rect.right,rect.bottom,hMemDC,0,0,SRCCOPY
        invoke DeleteDC,hMemDC
        invoke EndPaint,hWnd,ADDR ps
.ELSEIF uMsg==WM_DESTROY
        invoke DeleteObject,hBitmap
        invoke PostQuitMessage,NULL
.ELSE
        invoke DefWindowProc,hWnd,uMsg,wParam,lParam
        ret
.ENDIF
        xor    eax,eax
        ret
WndProc ENDP

END start

;-----------------------------------------------------------------------
; The resource script
;-----------------------------------------------------------------------
#define IDB_MAIN 1
IDB_MAIN BITMAP "tweety78.bmp"

Analysis:

There is not much to analyze in this tutorial ;)

#define IDB_MAIN 1
IDB_MAIN BITMAP "tweety78.bmp"

Define a constant named IDB_MAIN, assign 1 as its value. And then use that constant as the bitmap resource identifier. The bitmap file to be included in the resource is "tweety78.bmp" which resides in the same folder as the resource script.

.IF uMsg==WM_CREATE
        invoke LoadBitmap,hInstance,IDB_MAIN
        mov    hBitmap,eax

In response to WM_CREATE, we call LoadBitmap to load the bitmap from the resource, passing the bitmap's resource identifier as the second parameter to the API. We get the handle to the bitmap when the function returns.

Now that the bitmap is loaded, we can paint it in the client area of our main window.

.ELSEIF uMsg==WM_PAINT
        invoke BeginPaint,hWnd,ADDR ps
        mov    hdc,eax
        invoke CreateCompatibleDC,hdc
        mov    hMemDC,eax
        invoke SelectObject,hMemDC,hBitmap
        invoke GetClientRect,hWnd,ADDR rect
        invoke BitBlt,hdc,0,0,rect.right,rect.bottom,hMemDC,0,0,SRCCOPY
        invoke DeleteDC,hMemDC
        invoke EndPaint,hWnd,ADDR ps

We choose to paint the bitmap in response to WM_PAINT message. We first call BeginPaint to obtain the handle to the device context. Then we create a compatible memory DC with CreateCompatibleDC. Next select the bitmap into the memory DC with SelectObject. Determine the dimension of the client area with GetClientRect. Now we can display the bitmap in the client area by calling BitBlt which copies the bitmap from the memory DC to the real DC. When the painting is done, we have no further need for the memory DC so we delete it with DeleteDC. End painting session with EndPaint.

.ELSEIF uMsg==WM_DESTROY
        invoke DeleteObject,hBitmap
        invoke PostQuitMessage,NULL

When we don't need the bitmap anymore, we delete it with DeleteObject

Tutorial 24: Windows Hooks

Overview

Tutorial 26: Splash Screen