iczelion tut25[2]

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
1. 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.
1. 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