how to scroll a painted region? - c++

Question

I want to scroll a painted region. I use the CS_OWNDC style with WS_HSCROLL | WS_VSCROLL.My WM_PAINT block draws a line outgoing from the visible region (I suspect that I need to increase the buffer somehow).How can I make this?Please give me an example
PS. Block of code WM_HSCROLL incorrect working i don't know how to fix this.
My code:
// C++ WINAPI LEARN
#include <Windows.h>
WNDCLASS windowClass;
HDC hdc;
PAINTSTRUCT ps;
int hScroll, vScroll;
bool first = true;
LRESULT CALLBACK WndProc(HWND hWindow, UINT typeMessage, WPARAM wParam, LPARAM lParam)
{
switch (typeMessage)
{
case WM_PAINT:
hdc = BeginPaint(hWindow, &ps);
//HERE ANYTHING DRAW CODE (words, line any figure)
//(draw line out visible region)
if (first == true)
{
first = false;
MoveToEx(hdc, 5, 5, NULL);
LineTo(hdc, 900, 500);
}
EndPaint(hWindow, &ps);
break;
case WM_HSCROLL:
//SCOLLBAR NOT JOB!
if (LOWORD(wParam) == SB_LINERIGHT) // this block not job!!!
{
hScroll++;
}
else if (LOWORD(wParam) == SB_LINELEFT) // this block not job!!!
{
hScroll--;
}
else if (LOWORD(wParam) == SB_THUMBTRACK)
{
hScroll=HIWORD(wParam);
}
SetScrollPos(hWindow, SB_HORZ, hScroll, FALSE);
ScrollWindow(hWindow, hScroll, vScroll, NULL, NULL);
break;
case WM_DESTROY:
PostQuitMessage(0);
return 0;
break;
}
return DefWindowProc(hWindow, typeMessage, wParam, lParam);
}
int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstanse, LPSTR LpszCmdParam, int nCmdShow)
{
//CREATE WINDOW
windowClass = { 0 };
windowClass.lpszClassName = "ScrollTest";
windowClass.hInstance = hInstance;
windowClass.lpfnWndProc = WndProc;
windowClass.style = CS_OWNDC;
//REGISTER CLASS
RegisterClass(&windowClass);
HWND myWindow = ::CreateWindowEx(
0,
"ScrollTest",
"Scroll Paint",
WS_VISIBLE | WS_OVERLAPPEDWINDOW | WS_HSCROLL | WS_VSCROLL,
100, 100,
500, 500,
NULL,
0,
hInstance,
0
);
//TRANSLATE MESSAGE
for (MSG windowMessage; GetMessage(&windowMessage, NULL, 0, 0);)
{
DispatchMessage(&windowMessage); //TRANSLATE MESSAGES
TranslateMessage(&windowMessage); //TRANSLATE KEYS
}
}

Answer 1

Based on the demo, I modified part of the code and it works normally.
Some code:
LRESULT CALLBACK MyTextWindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
HDC hdc;
PAINTSTRUCT ps;
TEXTMETRIC tm;
SCROLLINFO si;
// These variables are required to display text.
static int xChar; // horizontal scrolling unit
static int yChar; // vertical scrolling unit
static int xPos; // current horizontal scrolling position
static int yPos; // current vertical scrolling position
int x, y; // horizontal and vertical coordinates
// Create an array of lines to display.
switch (uMsg)
{
case WM_CREATE:
// Get the handle to the client area's device context.
hdc = GetDC(hwnd);
// Extract font dimensions from the text metrics.
GetTextMetrics(hdc, &tm);
xChar = tm.tmAveCharWidth;
yChar = tm.tmHeight + tm.tmExternalLeading;
// Free the device context.
ReleaseDC(hwnd, hdc);
return 0;
case WM_HSCROLL:
// Get all the vertial scroll bar information.
si.cbSize = sizeof(si);
si.fMask = SIF_ALL;
// Save the position for comparison later on.
GetScrollInfo(hwnd, SB_HORZ, &si);
xPos = si.nPos;
switch (LOWORD(wParam))
{
// User clicked the left arrow.
case SB_LINELEFT:
si.nPos -= 1;
break;
// User clicked the right arrow.
case SB_LINERIGHT:
si.nPos += 1;
break;
// User clicked the scroll bar shaft left of the scroll box.
case SB_PAGELEFT:
si.nPos -= si.nPage;
break;
// User clicked the scroll bar shaft right of the scroll box.
case SB_PAGERIGHT:
si.nPos += si.nPage;
break;
// User dragged the scroll box.
case SB_THUMBTRACK:
si.nPos = si.nTrackPos;
break;
default:
break;
}
// Set the position and then retrieve it. Due to adjustments
// by Windows it may not be the same as the value set.
si.fMask = SIF_POS;
SetScrollInfo(hwnd, SB_HORZ, &si, TRUE);
GetScrollInfo(hwnd, SB_HORZ, &si);
// If the position has changed, scroll the window.
if (si.nPos != xPos)
{
ScrollWindow(hwnd, xChar * (xPos - si.nPos), 0, NULL, NULL);
}
return 0;
case WM_VSCROLL:
// Get all the vertial scroll bar information.
si.cbSize = sizeof(si);
si.fMask = SIF_ALL;
GetScrollInfo(hwnd, SB_VERT, &si);
// Save the position for comparison later on.
yPos = si.nPos;
switch (LOWORD(wParam))
{
// User clicked the HOME keyboard key.
case SB_TOP:
si.nPos = si.nMin;
break;
// User clicked the END keyboard key.
case SB_BOTTOM:
si.nPos = si.nMax;
break;
// User clicked the top arrow.
case SB_LINEUP:
si.nPos -= 1;
break;
// User clicked the bottom arrow.
case SB_LINEDOWN:
si.nPos += 1;
break;
// User clicked the scroll bar shaft above the scroll box.
case SB_PAGEUP:
si.nPos -= si.nPage;
break;
// User clicked the scroll bar shaft below the scroll box.
case SB_PAGEDOWN:
si.nPos += si.nPage;
break;
// User dragged the scroll box.
case SB_THUMBTRACK:
si.nPos = si.nTrackPos;
break;
default:
break;
}
// Set the position and then retrieve it. Due to adjustments
// by Windows it may not be the same as the value set.
si.fMask = SIF_POS;
SetScrollInfo(hwnd, SB_VERT, &si, TRUE);
GetScrollInfo(hwnd, SB_VERT, &si);
// If the position has changed, scroll window and update it.
if (si.nPos != yPos)
{
ScrollWindow(hwnd, 0, yChar * (yPos - si.nPos), NULL, NULL);
UpdateWindow(hwnd);
}
return 0;
case WM_PAINT:
// Prepare the window for painting.
hdc = BeginPaint(hwnd, &ps);
// Get vertical scroll bar position.
si.cbSize = sizeof(si);
si.fMask = SIF_POS;
GetScrollInfo(hwnd, SB_VERT, &si);
yPos = si.nPos;
// Get horizontal scroll bar position.
GetScrollInfo(hwnd, SB_HORZ, &si);
xPos = si.nPos;
x = xChar * (1 - xPos);
y = yChar * (1 - yPos);
MoveToEx(hdc, 5 + x, 5 + y, NULL);
LineTo(hdc, 900 + x, 500 + y);
// Indicate that painting is finished.
EndPaint(hwnd, &ps);
return 0;
case WM_DESTROY:
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
Debug: