Win32 API: transparency doesn't work - c++

Question

I wrote a simple program; it's made of a main window and TextBox window above it. TextBox is 50% transparent. When TextBox gets a message, it draws a blue line on the main window.
The problem is that "transparent" actually is not transparent at all. If the blue line crosses a text in TextBox, the text just erased, despite the fact that the text is above. And vice versa: if I start typing, a part of the line in a row of a text just disappears instead of shine through.
Is this a bug? Or am I missing something?
#include <windows.h>
#include <stdio.h>
#define IDC_MAIN_EDIT 101
void DrawInWindow(HWND hWndToPaint){
HDC hdc = GetDC(hWndToPaint);
if(!hdc)printf("Invalid handle\n");
HPEN hPen = CreatePen(PS_SOLID,5,RGB(0, 0, 255));
SelectObject(hdc, hPen);
static float x=620, y=1, tg=0.5, ctg=2;
static int Xone = 1, Yone = 1;//depending on later recalculation this may become negative
MoveToEx(hdc,(int)x,(int)y,NULL);
if(tg<1){
y+=tg;
x+=Xone;
}else{
y+=Yone;
x+=ctg;
}
if(!LineTo(hdc, (int)x, (int)y) )printf("There are paint problem\n");
ReleaseDC(hWndToPaint,hdc);
//Now recalculate direction
RECT WndRect;
GetClientRect(hWndToPaint,&WndRect);
if(x>=WndRect.right){
if(ctg>0)ctg*=-1;//make negative
Xone=-1;
}
if(x<=WndRect.left){
if(ctg<0)ctg*=-1;//make positive
Xone=1;
}
if(y>=WndRect.bottom){
if(tg>0)tg*=-1;//make negative
Yone=-1;
}
if(y<=WndRect.top){
if(tg<0)tg*=-1;//make positive
Yone=1;
}
}
int CALLBACK EnumWindowsFunc(HWND hWnd, LPARAM lParam){
DrawInWindow(hWnd);
return false;
}
void PaintInMainWnd(){
EnumWindows(EnumWindowsFunc,0L);//Getting the handle of main window to draw
}
LRESULT __stdcall MyMainCallBckProcedure( HWND window, unsigned msg, WPARAM wp, LPARAM lp ){
switch(msg){
case WM_KEYDOWN:
if(wp == VK_ESCAPE)PostQuitMessage(0);
break;
case WM_DESTROY:
printf("\ndestroying window\n");
PostQuitMessage(0);
return 0;
case WM_SIZE:{
HWND hEdit;
RECT rcClient;
GetClientRect(window, &rcClient);
hEdit = GetDlgItem(window, IDC_MAIN_EDIT);
SetWindowPos(hEdit, NULL, 0, 0, rcClient.right, rcClient.bottom, SWP_NOZORDER);
break;
}
default:
return DefWindowProc( window, msg, wp, lp ) ;
}
}
WNDPROC lpEditWndProc;
LRESULT CALLBACK MyEditCallBckProcedure(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam){
if( (uMsg == WM_CHAR) && (wParam == VK_ESCAPE) )
{
PostQuitMessage(0);
return 0;
}
PaintInMainWnd();
lpEditWndProc(hWnd, uMsg, wParam, lParam);
}
bool CreateWindows(){
const char* const myclass = "myclass";
WNDCLASSEX wndclass = { sizeof(WNDCLASSEX), CS_DBLCLKS, MyMainCallBckProcedure,
0, 0, GetModuleHandle(0), LoadIcon(0,IDI_APPLICATION),
LoadCursor(0,IDC_ARROW), HBRUSH(COLOR_WINDOW+1),
0, myclass, LoadIcon(0,IDI_APPLICATION) };
if(RegisterClassEx(&wndclass)<0){
printf("ERR: in registering window class\n");
return false;
}
//Creating window
HWND window = CreateWindowEx( 0, myclass, "title",
WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT,
640, 480, 0, 0, GetModuleHandle(0), 0 );
if(!window){
printf("ERR: in creating window\n");
return false;
}
ShowWindow( window, SW_SHOWDEFAULT );
//creating TextBox on the window
HFONT hfDefault;
HWND hEdit;
hEdit = CreateWindowEx(0, "edit", "",
WS_CHILD | WS_VISIBLE | WS_VSCROLL | WS_HSCROLL | ES_MULTILINE | ES_AUTOVSCROLL | ES_AUTOHSCROLL,
CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
window, (HMENU)IDC_MAIN_EDIT, GetModuleHandle(NULL), NULL);
if(hEdit == NULL){
MessageBox(window, "Could not create edit box.", "Error", MB_OK | MB_ICONERROR);
return false;
}
hfDefault = (HFONT)GetStockObject(DEFAULT_GUI_FONT);
SendMessage(hEdit, WM_SETFONT, (WPARAM)hfDefault, MAKELPARAM(FALSE, 0));
//Now resize TextBox to fill whole parent window
RECT RectSize;
GetClientRect(window,&RectSize);
hEdit = GetDlgItem(window,IDC_MAIN_EDIT);
SetWindowPos(hEdit, 0,0,0,RectSize.right,RectSize.bottom,SWP_NOZORDER);
//Let's try to catch some messages in TextBox...
lpEditWndProc = (WNDPROC)SetWindowLongPtr(hEdit, GWL_WNDPROC, (LONG_PTR)&MyEditCallBckProcedure);
//Making hEdit transparent
SetWindowLongPtr(hEdit,GWL_EXSTYLE, WS_EX_LAYERED | GetWindowLongPtr(hEdit, GWL_EXSTYLE) );
SetLayeredWindowAttributes(hEdit, 0, (255*50)/100, LWA_ALPHA);
return true;
//###
}
int main(){
if(!CreateWindows() ){printf("Something gone wrong\n");return 1;}
MSG msg;
while(GetMessage(&msg,0,0,0) ){
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
Don't know is it important, but I should also mention, that I have tested only under Ubuntu with Wine, as my Windows is screwed up by this bug. Anyway, I hope the problem is not in Wine itself.
And sorry for amount of code, I really don't know what to remove to make it smaller.

Answer 1

I found the workaround. I created background top level window, and made foreground window 50% trasparent. I draw the lines in background window. If the front window moved or resized, the back window reacts accordingly with help of WM_WINDOWPOSCHANGED message, it sent on every little move/resize.
Anyway, this workaround is little dirty because of:
Linux/wine specific problems: 1) Display Manager do not decorate transparent window of wine(but this could be evaded by making second window 0% transparent) 2) Dragged window wobbling, but the second moving straight. All OS specific problem: second window is visible in the taskbar. Theoretically the last could be avoided by adding WS_EX_TOOLWINDOW to unowned window. The quote
To prevent the window button from being placed on the taskbar, create
the unowned window with the WS_EX_TOOLWINDOW extended style.
But, at least, in wine it doesn't work. Well, I hope this is a bug :)
#include <windows.h>
#include <stdio.h>
#define IDC_MAIN_EDIT 101
HWND hBackWnd;
void DrawInWindow(HWND hWndToPaint){
HDC hdc = GetDC(hWndToPaint);
if(!hdc)printf("Invalid handle\n");
HPEN hPen = CreatePen(PS_SOLID,5,RGB(0, 0, 255));
SelectObject(hdc, hPen);
static float x=620, y=1, tg=0.5, ctg=2;
static int Xone = 1, Yone = 1;//depending on later recalculation this may become negative
MoveToEx(hdc,(int)x,(int)y,NULL);
if(tg<1){
y+=tg;
x+=Xone;
}else{
y+=Yone;
x+=ctg;
}
if(!LineTo(hdc, (int)x, (int)y) )printf("There are paint problem\n");
ReleaseDC(hWndToPaint,hdc);
//Now recalculate direction
RECT WndRect;
GetClientRect(hWndToPaint,&WndRect);
if(x>=WndRect.right){
if(ctg>0)ctg*=-1;//make negative
Xone=-1;
}
if(x<=WndRect.left){
if(ctg<0)ctg*=-1;//make positive
Xone=1;
}
if(y>=WndRect.bottom){
if(tg>0)tg*=-1;//make negative
Yone=-1;
}
if(y<=WndRect.top){
if(tg<0)tg*=-1;//make positive
Yone=1;
}
}
LRESULT __stdcall MyMainCallBckProcedure( HWND window, unsigned msg, WPARAM wp, LPARAM lp ){
switch(msg){
case WM_KEYDOWN:
if(wp == VK_ESCAPE)PostQuitMessage(0);
break;
case WM_DESTROY:
printf("\ndestroying window\n");
PostQuitMessage(0);
return 0;
case WM_SIZE:
HWND hEdit;
RECT rcClient;
GetClientRect(window, &rcClient);
hEdit = GetDlgItem(window, IDC_MAIN_EDIT);
SetWindowPos(hEdit, NULL, 0, 0, rcClient.right, rcClient.bottom, SWP_NOZORDER);
break;
case WM_WINDOWPOSCHANGED:{//LPARAM is a ptr to WINDOWPOS
RECT BckWndRect;
if(!GetWindowRect(hBackWnd, &BckWndRect) )printf("ERR: getting backwnd rectangle\n");
bool IsRepaint;
WINDOWPOS* pNewPos = (WINDOWPOS*)lp;
if(BckWndRect.left+BckWndRect.right != pNewPos->cx
|| BckWndRect.top+BckWndRect.bottom != pNewPos->cy)IsRepaint = true;
else IsRepaint = false;
MoveWindow(hBackWnd, pNewPos->x, pNewPos->y, pNewPos->cx, pNewPos->cy, IsRepaint);
break;
}
default:
return DefWindowProc( window, msg, wp, lp ) ;
}
}
WNDPROC lpEditWndProc;
LRESULT CALLBACK MyEditCallBckProcedure(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam){
if( (uMsg == WM_CHAR) && (wParam == VK_ESCAPE) )
{
PostQuitMessage(0);
return 0;
}
DrawInWindow(hBackWnd);
lpEditWndProc(hWnd, uMsg, wParam, lParam);
}
bool CreateWindows(){
//creating back window
const char* backwnd = "backwnd";
WNDCLASSEX backwndclass = { sizeof(WNDCLASSEX), CS_DBLCLKS, MyMainCallBckProcedure,
0, 0, GetModuleHandle(0), LoadIcon(0,IDI_APPLICATION),
LoadCursor(0,IDC_ARROW), HBRUSH(COLOR_WINDOW+1),
0, backwnd, LoadIcon(0,IDI_APPLICATION) };
if(RegisterClassEx(&backwndclass)<0){
printf("ERR: in registering second window class\n");
return false;
}
hBackWnd = CreateWindowEx( 0, backwnd, "title", WS_EX_TOOLWINDOW |
WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT,
640, 480, 0, 0, GetModuleHandle(0), 0 );
if(!hBackWnd){
printf("ERR: in creating background window\n");
return false;
}
ShowWindow( hBackWnd, SW_SHOWDEFAULT );
//Creating front window
const char* const frontwnd = "frontwnd";
WNDCLASSEX wndclass = { sizeof(WNDCLASSEX), CS_DBLCLKS, MyMainCallBckProcedure,
0, 0, GetModuleHandle(0), LoadIcon(0,IDI_APPLICATION),
LoadCursor(0,IDC_ARROW), HBRUSH(COLOR_WINDOW+1),
0, frontwnd, LoadIcon(0,IDI_APPLICATION) };
if(RegisterClassEx(&wndclass)<0){
printf("ERR: in registering foreground window class\n");
return false;
}
HWND window = CreateWindowEx( 0, frontwnd, "title",
WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT,
640, 480, 0, 0, GetModuleHandle(0), 0 );
if(!window){
printf("ERR: in creating foreground window\n");
return false;
}
ShowWindow( window, SW_SHOWDEFAULT );
//creating textbox
HWND hEdit = CreateWindowEx( 0, "edit", "", WS_CHILD | WS_VISIBLE | WS_VSCROLL | WS_HSCROLL
| ES_MULTILINE | ES_AUTOVSCROLL, CW_USEDEFAULT, CW_USEDEFAULT, 640,
480, window, (HMENU)IDC_MAIN_EDIT, GetModuleHandle(0), 0 );
HFONT hfDefault = (HFONT)GetStockObject(DEFAULT_GUI_FONT);
SendMessage(hEdit, WM_SETFONT, (WPARAM)hfDefault, MAKELPARAM(FALSE, 0));
//Let's try to catch some messages in TextBox...
lpEditWndProc = (WNDPROC)SetWindowLongPtr(hEdit, GWL_WNDPROC, (LONG_PTR)&MyEditCallBckProcedure);
//Making foreground window transparent
SetWindowLongPtr(window,GWL_EXSTYLE, WS_EX_LAYERED | GetWindowLongPtr(window, GWL_EXSTYLE) );
SetLayeredWindowAttributes(window, 0, (255*50)/100, LWA_ALPHA);
return true;
//###
}
int main(){
if(!CreateWindows() ){printf("Something gone wrong\n");return 1;}
MSG msg;
while(GetMessage(&msg,0,0,0) ){
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}