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BufferedGraphicsContext.cs
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BufferedGraphicsContext.cs
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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Threading;
using static Interop;
namespace System.Drawing;
/// <summary>
/// The BufferedGraphicsContext class can be used to perform standard double buffer rendering techniques.
/// </summary>
public sealed class BufferedGraphicsContext : IDisposable
{
private Size _maximumBuffer;
private Size _bufferSize = Size.Empty;
private Size _virtualSize;
private Point _targetLoc;
private IntPtr _compatDC;
private IntPtr _dib;
private IntPtr _oldBitmap;
private Graphics? _compatGraphics;
private BufferedGraphics? _buffer;
private int _busy;
private bool _invalidateWhenFree;
private const int BufferFree = 0; // The graphics buffer is free to use.
private const int BufferBusyPainting = 1; // The graphics buffer is busy being created/painting.
private const int BufferBusyDisposing = 2; // The graphics buffer is busy disposing.
/// <summary>
/// Basic constructor.
/// </summary>
public BufferedGraphicsContext()
{
// By defualt, the size of our maxbuffer will be 3 x standard button size.
_maximumBuffer.Width = 75 * 3;
_maximumBuffer.Height = 32 * 3;
}
/// <summary>
/// Allows you to set the maximum width and height of the buffer that will be retained in memory.
/// You can allocate a buffer of any size, however any request for a buffer that would have a total
/// memory footprint larger that the maximum size will be allocated temporarily and then discarded
/// with the BufferedGraphics is released.
/// </summary>
public Size MaximumBuffer
{
get => _maximumBuffer;
set
{
if (value.Width <= 0 || value.Height <= 0)
{
throw new ArgumentException(SR.Format(SR.InvalidArgumentValue, nameof(MaximumBuffer), value), nameof(value));
}
// If we've been asked to decrease the size of the maximum buffer,
// then invalidate the older & larger buffer.
if (value.Width * value.Height < _maximumBuffer.Width * _maximumBuffer.Height)
{
Invalidate();
}
_maximumBuffer = value;
}
}
~BufferedGraphicsContext() => Dispose(false);
/// <summary>
/// Returns a BufferedGraphics that is matched for the specified target Graphics object.
/// </summary>
public BufferedGraphics Allocate(Graphics targetGraphics, Rectangle targetRectangle)
{
if (ShouldUseTempManager(targetRectangle))
{
return AllocBufferInTempManager(targetGraphics, IntPtr.Zero, targetRectangle);
}
return AllocBuffer(targetGraphics, IntPtr.Zero, targetRectangle);
}
/// <summary>
/// Returns a BufferedGraphics that is matched for the specified target HDC object.
/// </summary>
public BufferedGraphics Allocate(IntPtr targetDC, Rectangle targetRectangle)
{
if (ShouldUseTempManager(targetRectangle))
{
return AllocBufferInTempManager(null, targetDC, targetRectangle);
}
return AllocBuffer(null, targetDC, targetRectangle);
}
/// <summary>
/// Returns a BufferedGraphics that is matched for the specified target HDC object.
/// </summary>
private BufferedGraphics AllocBuffer(Graphics? targetGraphics, IntPtr targetDC, Rectangle targetRectangle)
{
int oldBusy = Interlocked.CompareExchange(ref _busy, BufferBusyPainting, BufferFree);
// In the case were we have contention on the buffer - i.e. two threads
// trying to use the buffer at the same time, we just create a temp
// buffermanager and have the buffer dispose of it when it is done.
//
if (oldBusy != BufferFree)
{
return AllocBufferInTempManager(targetGraphics, targetDC, targetRectangle);
}
Graphics surface;
_targetLoc = new Point(targetRectangle.X, targetRectangle.Y);
try
{
if (targetGraphics != null)
{
IntPtr destDc = targetGraphics.GetHdc();
try
{
surface = CreateBuffer(destDc, targetRectangle.Width, targetRectangle.Height);
}
finally
{
targetGraphics.ReleaseHdcInternal(destDc);
}
}
else
{
surface = CreateBuffer(targetDC, targetRectangle.Width, targetRectangle.Height);
}
_buffer = new BufferedGraphics(surface, this, targetGraphics, targetDC, _targetLoc, _virtualSize);
}
catch
{
// Free the buffer so it can be disposed.
_busy = BufferFree;
throw;
}
return _buffer;
}
/// <summary>
/// Returns a BufferedGraphics that is matched for the specified target HDC object.
/// </summary>
private static BufferedGraphics AllocBufferInTempManager(Graphics? targetGraphics, IntPtr targetDC, Rectangle targetRectangle)
{
BufferedGraphicsContext? tempContext = null;
BufferedGraphics? tempBuffer = null;
try
{
tempContext = new BufferedGraphicsContext();
tempBuffer = tempContext.AllocBuffer(targetGraphics, targetDC, targetRectangle);
tempBuffer.DisposeContext = true;
}
finally
{
if (tempContext != null && (tempBuffer == null || (tempBuffer != null && !tempBuffer.DisposeContext)))
{
tempContext.Dispose();
}
}
return tempBuffer;
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
/// <summary>
/// This routine allows us to control the point were we start using throw away
/// managers for painting. Since the buffer manager stays around (by default)
/// for the life of the app, we don't want to consume too much memory
/// in the buffer. However, re-allocating the buffer for small things (like
/// buttons, labels, etc) will hit us on runtime performance.
/// </summary>
private bool ShouldUseTempManager(Rectangle targetBounds)
{
return (targetBounds.Width * targetBounds.Height) > (MaximumBuffer.Width * MaximumBuffer.Height);
}
/// <summary>
/// Fills in the fields of a BITMAPINFO so that we can create a bitmap
/// that matches the format of the display.
///
/// This is done by creating a compatible bitmap and calling GetDIBits
/// to return the color masks. This is done with two calls. The first
/// call passes in biBitCount = 0 to GetDIBits which will fill in the
/// base BITMAPINFOHEADER data. The second call to GetDIBits (passing
/// in the BITMAPINFO filled in by the first call) will return the color
/// table or bitmasks, as appropriate.
/// </summary>
/// <returns>True if successful, false otherwise.</returns>
private unsafe bool FillBitmapInfo(IntPtr hdc, IntPtr hpal, ref Gdi32.BITMAPINFO_FLAT pbmi)
{
IntPtr hbm = IntPtr.Zero;
bool bRet = false;
try
{
// Create a dummy bitmap from which we can query color format info
// about the device surface.
hbm = Gdi32.CreateCompatibleBitmap(new HandleRef(null, hdc), 1, 1);
if (hbm == IntPtr.Zero)
{
throw new OutOfMemoryException(SR.GraphicsBufferQueryFail);
}
pbmi.bmiHeader_biSize = sizeof(NativeMethods.BITMAPINFOHEADER);
// Call first time to fill in BITMAPINFO header.
Gdi32.GetDIBits(
new HandleRef(null, hdc),
new HandleRef(null, hbm),
0,
0,
IntPtr.Zero,
ref pbmi,
NativeMethods.DIB_RGB_COLORS);
if (pbmi.bmiHeader_biBitCount <= 8)
{
bRet = FillColorTable(hdc, hpal, ref pbmi);
}
else
{
if (pbmi.bmiHeader_biCompression == NativeMethods.BI_BITFIELDS)
{
// Call a second time to get the color masks.
Gdi32.GetDIBits(
new HandleRef(null, hdc),
new HandleRef(null, hbm),
0,
pbmi.bmiHeader_biHeight,
IntPtr.Zero,
ref pbmi,
NativeMethods.DIB_RGB_COLORS);
}
bRet = true;
}
}
finally
{
if (hbm != IntPtr.Zero)
{
Gdi32.DeleteObject(hbm);
}
}
return bRet;
}
/// <summary>
/// Initialize the color table of the BITMAPINFO pointed to by pbmi. Colors
/// are set to the current system palette.
///
/// Note: call only valid for displays of 8bpp or less.
/// </summary>
/// <returns>True is successful, false otherwise.</returns>
private unsafe bool FillColorTable(IntPtr hdc, IntPtr hpal, ref Gdi32.BITMAPINFO_FLAT pbmi)
{
byte[] aj = new byte[sizeof(NativeMethods.PALETTEENTRY) * 256];
fixed (byte* pcolors = pbmi.bmiColors)
{
fixed (byte* ppal = aj)
{
NativeMethods.RGBQUAD* prgb = (NativeMethods.RGBQUAD*)pcolors;
NativeMethods.PALETTEENTRY* lppe = (NativeMethods.PALETTEENTRY*)ppal;
int cColors = 1 << pbmi.bmiHeader_biBitCount;
if (cColors <= 256)
{
// Note: we don't support 4bpp displays.
uint palRet;
IntPtr palHalftone = IntPtr.Zero;
if (hpal == IntPtr.Zero)
{
palHalftone = Graphics.GetHalftonePalette();
palRet = Gdi32.GetPaletteEntries(new HandleRef(null, palHalftone), 0, cColors, aj);
}
else
{
palRet = Gdi32.GetPaletteEntries(new HandleRef(null, hpal), 0, cColors, aj);
}
if (palRet != 0)
{
for (int i = 0; i < cColors; i++)
{
prgb[i].rgbRed = lppe[i].peRed;
prgb[i].rgbGreen = lppe[i].peGreen;
prgb[i].rgbBlue = lppe[i].peBlue;
prgb[i].rgbReserved = 0;
}
return true;
}
}
}
}
return false;
}
/// <summary>
/// Returns a Graphics object representing a buffer.
/// </summary>
private Graphics CreateBuffer(IntPtr src, int width, int height)
{
// Create the compat DC.
_busy = BufferBusyDisposing;
DisposeDC();
_busy = BufferBusyPainting;
_compatDC = Gdi32.CreateCompatibleDC(src);
// Recreate the bitmap if necessary.
if (width > _bufferSize.Width || height > _bufferSize.Height)
{
int optWidth = Math.Max(width, _bufferSize.Width);
int optHeight = Math.Max(height, _bufferSize.Height);
_busy = BufferBusyDisposing;
DisposeBitmap();
_busy = BufferBusyPainting;
IntPtr pvbits = IntPtr.Zero;
_dib = CreateCompatibleDIB(src, IntPtr.Zero, optWidth, optHeight, ref pvbits);
_bufferSize = new Size(optWidth, optHeight);
}
// Select the bitmap.
_oldBitmap = Kernel32.SelectObject(new HandleRef(this, _compatDC), new HandleRef(this, _dib));
// Create compat graphics.
_compatGraphics = Graphics.FromHdcInternal(_compatDC);
_compatGraphics.TranslateTransform(-_targetLoc.X, -_targetLoc.Y);
_virtualSize = new Size(width, height);
return _compatGraphics;
}
/// <summary>
/// Create a DIB section with an optimal format w.r.t. the specified hdc.
///
/// If DIB <= 8bpp, then the DIB color table is initialized based on the
/// specified palette. If the palette handle is NULL, then the system
/// palette is used.
///
/// Note: The hdc must be a direct DC (not an info or memory DC).
///
/// Note: On palettized displays, if the system palette changes the
/// UpdateDIBColorTable function should be called to maintain
/// the identity palette mapping between the DIB and the display.
/// </summary>
/// <returns>A valid bitmap handle if successful, IntPtr.Zero otherwise.</returns>
private IntPtr CreateCompatibleDIB(IntPtr hdc, IntPtr hpal, int ulWidth, int ulHeight, ref IntPtr ppvBits)
{
if (hdc == IntPtr.Zero)
{
throw new ArgumentNullException(nameof(hdc));
}
IntPtr hbmRet = IntPtr.Zero;
Gdi32.BITMAPINFO_FLAT pbmi = default;
// Validate hdc.
Gdi32.ObjectType objType = Gdi32.GetObjectType(hdc);
switch (objType)
{
case Gdi32.ObjectType.OBJ_DC:
case Gdi32.ObjectType.OBJ_METADC:
case Gdi32.ObjectType.OBJ_MEMDC:
case Gdi32.ObjectType.OBJ_ENHMETADC:
break;
default:
throw new ArgumentException(SR.DCTypeInvalid);
}
if (FillBitmapInfo(hdc, hpal, ref pbmi))
{
// Change bitmap size to match specified dimensions.
pbmi.bmiHeader_biWidth = ulWidth;
pbmi.bmiHeader_biHeight = ulHeight;
if (pbmi.bmiHeader_biCompression == NativeMethods.BI_RGB)
{
pbmi.bmiHeader_biSizeImage = 0;
}
else
{
if (pbmi.bmiHeader_biBitCount == 16)
{
pbmi.bmiHeader_biSizeImage = ulWidth * ulHeight * 2;
}
else if (pbmi.bmiHeader_biBitCount == 32)
{
pbmi.bmiHeader_biSizeImage = ulWidth * ulHeight * 4;
}
else
{
pbmi.bmiHeader_biSizeImage = 0;
}
}
pbmi.bmiHeader_biClrUsed = 0;
pbmi.bmiHeader_biClrImportant = 0;
// Create the DIB section. Let Win32 allocate the memory and return
// a pointer to the bitmap surface.
hbmRet = Gdi32.CreateDIBSection(new HandleRef(null, hdc), ref pbmi, NativeMethods.DIB_RGB_COLORS, ref ppvBits, IntPtr.Zero, 0);
Win32Exception? ex = null;
if (hbmRet == IntPtr.Zero)
{
ex = new Win32Exception(Marshal.GetLastWin32Error());
}
if (ex != null)
{
throw ex;
}
}
return hbmRet;
}
/// <summary>
/// Disposes the DC, but leaves the bitmap alone.
/// </summary>
private void DisposeDC()
{
if (_oldBitmap != IntPtr.Zero && _compatDC != IntPtr.Zero)
{
Kernel32.SelectObject(new HandleRef(this, _compatDC), new HandleRef(this, _oldBitmap));
_oldBitmap = IntPtr.Zero;
}
if (_compatDC != IntPtr.Zero)
{
Gdi32.DeleteDC(new HandleRef(this, _compatDC));
_compatDC = IntPtr.Zero;
}
}
/// <summary>
/// Disposes the bitmap, will ASSERT if bitmap is being used (checks oldbitmap). if ASSERTed, call DisposeDC() first.
/// </summary>
private void DisposeBitmap()
{
if (_dib != IntPtr.Zero)
{
Debug.Assert(_oldBitmap == IntPtr.Zero);
Gdi32.DeleteObject(new HandleRef(this, _dib));
_dib = IntPtr.Zero;
}
}
/// <summary>
/// Disposes of the Graphics buffer.
/// </summary>
private void Dispose(bool disposing)
{
int oldBusy = Interlocked.CompareExchange(ref _busy, BufferBusyDisposing, BufferFree);
if (disposing)
{
if (oldBusy == BufferBusyPainting)
{
throw new InvalidOperationException(SR.GraphicsBufferCurrentlyBusy);
}
if (_compatGraphics != null)
{
_compatGraphics.Dispose();
_compatGraphics = null;
}
}
DisposeDC();
DisposeBitmap();
if (_buffer != null)
{
_buffer.Dispose();
_buffer = null;
}
_bufferSize = Size.Empty;
_virtualSize = Size.Empty;
_busy = BufferFree;
}
/// <summary>
/// Invalidates the cached graphics buffer.
/// </summary>
public void Invalidate()
{
int oldBusy = Interlocked.CompareExchange(ref _busy, BufferBusyDisposing, BufferFree);
// If we're not busy with our buffer, lets clean it up now
if (oldBusy == BufferFree)
{
Dispose();
_busy = BufferFree;
}
else
{
// This will indicate to free the buffer as soon as it becomes non-busy.
_invalidateWhenFree = true;
}
}
/// <summary>
/// Returns a Graphics object representing a buffer.
/// </summary>
internal void ReleaseBuffer()
{
_buffer = null;
if (_invalidateWhenFree)
{
// Clears everything including the bitmap.
_busy = BufferBusyDisposing;
Dispose();
}
else
{
// Otherwise, just dispose the DC. A new one will be created next time.
_busy = BufferBusyDisposing;
// Only clears out the DC.
DisposeDC();
}
_busy = BufferFree;
}
}