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[platform-swt-dev] SWT OpenGL Shared Contexts

For larger OpenGL applications, the feature to share OpenGL contexts is missing. As a work-around, we adapted the GLCanvas code, and added an additional constructor that takes a GLCanvas argument, whose context is then used as the shared context. As an example, I've pasted an excerpt for the Linux/GTK case. We use this for other platforms too, and it works great. It would be nice to see this (or a similar possibility) as part of standard SWT, as I think it's of general use. Also, it doesnt break API compatibility.

/Stefan
Software Architect, Procedural Inc.



/**
 * Create a GLCanvas widget using the attributes described in the GLData
 * object provided.
 *
 * @param parent a composite widget
 * @param style the bitwise OR'ing of widget styles
 * @param data the requested attributes of the GLCanvas
 * 
 *
 * @exception IllegalArgumentException
 * <ul><li>ERROR_NULL_ARGUMENT when the data is null
 *     <li>ERROR_UNSUPPORTED_DEPTH when the requested attributes cannot be provided</ul> 
 * </ul>
 */
public GLCanvas(Composite parent, int style, GLData caps) {
this(parent, style, caps, null);
}


/**
 * Create a GLCanvas widget using the attributes described in the GLData
 * object provided.
 *
 * @param parent a composite widget
 * @param style the bitwise OR'ing of widget styles
 * @param data the requested attributes of the GLCanvas
 * @param share shared canvas
 * 
 *
 * @exception IllegalArgumentException
 * <ul><li>ERROR_NULL_ARGUMENT when the data is null
 *     <li>ERROR_UNSUPPORTED_DEPTH when the requested attributes cannot be provided</ul> 
 * </ul>
 */
public GLCanvas (Composite parent, int style, GLData data, GLCanvas share) {
super (parent, style);
if (data == null) SWT.error (SWT.ERROR_NULL_ARGUMENT);
int glxAttrib [] = new int [MAX_ATTRIBUTES];
int pos = 0;
glxAttrib [pos++] = GLX.GLX_RGBA;
if (data.doubleBuffer) glxAttrib [pos++] = GLX.GLX_DOUBLEBUFFER;
if (data.stereo) glxAttrib [pos++] = GLX.GLX_STEREO;
if (data.redSize > 0) {
glxAttrib [pos++] = GLX.GLX_RED_SIZE;
glxAttrib [pos++] = data.redSize;
}
if (data.greenSize > 0) {
glxAttrib [pos++] = GLX.GLX_GREEN_SIZE;
glxAttrib [pos++] = data.greenSize;
}
if (data.blueSize > 0) {
glxAttrib [pos++] = GLX.GLX_BLUE_SIZE;
glxAttrib [pos++] = data.blueSize;
}
if (data.alphaSize > 0) {
glxAttrib [pos++] = GLX.GLX_ALPHA_SIZE;
glxAttrib [pos++] = data.alphaSize;
}
if (data.depthSize > 0) {
glxAttrib [pos++] = GLX.GLX_DEPTH_SIZE;
glxAttrib [pos++] = data.depthSize;
}
if (data.stencilSize > 0) {
glxAttrib [pos++] = GLX.GLX_STENCIL_SIZE;
glxAttrib [pos++] = data.stencilSize;
}
if (data.accumRedSize > 0) {
glxAttrib [pos++] = GLX.GLX_ACCUM_RED_SIZE;
glxAttrib [pos++] = data.accumRedSize;
}
if (data.accumGreenSize > 0) {
glxAttrib [pos++] = GLX.GLX_ACCUM_GREEN_SIZE;
glxAttrib [pos++] = data.accumGreenSize;
}
if (data.accumBlueSize > 0) {
glxAttrib [pos++] = GLX.GLX_ACCUM_BLUE_SIZE;
glxAttrib [pos++] = data.accumBlueSize;
}
if (data.accumAlphaSize > 0) {
glxAttrib [pos++] = GLX.GLX_ACCUM_ALPHA_SIZE;
glxAttrib [pos++] = data.accumAlphaSize;
}
if (data.sampleBuffers > 0) {
glxAttrib [pos++] = GLX.GLX_SAMPLE_BUFFERS;
glxAttrib [pos++] = data.sampleBuffers;
}
if (data.samples > 0) {
glxAttrib [pos++] = GLX.GLX_SAMPLES;
glxAttrib [pos++] = data.samples;
}
glxAttrib [pos++] = 0;
OS.gtk_widget_realize (handle);
int /*long*/ window = OS.GTK_WIDGET_WINDOW (handle);
int /*long*/ xDisplay = OS.gdk_x11_drawable_get_xdisplay (window);
int /*long*/ infoPtr = GLX.glXChooseVisual (xDisplay, OS.XDefaultScreen (xDisplay), glxAttrib);
if (infoPtr == 0) {
dispose ();
SWT.error (SWT.ERROR_UNSUPPORTED_DEPTH);
}
vinfo = new XVisualInfo ();
GLX.memmove (vinfo, infoPtr, XVisualInfo.sizeof);
OS.XFree (infoPtr);
int /*long*/ screen = OS.gdk_screen_get_default ();
int /*long*/ gdkvisual = OS.gdk_x11_screen_lookup_visual (screen, vinfo.visualid);

context = GLX.glXCreateContext (xDisplay, vinfo, share == null ? 0 : share.context, true);
if (context == 0) SWT.error (SWT.ERROR_NO_HANDLES);
GdkWindowAttr attrs = new GdkWindowAttr ();
attrs.width = 1;
attrs.height = 1;
attrs.event_mask = OS.GDK_KEY_PRESS_MASK | OS.GDK_KEY_RELEASE_MASK |
OS.GDK_FOCUS_CHANGE_MASK | OS.GDK_POINTER_MOTION_MASK |
OS.GDK_BUTTON_PRESS_MASK | OS.GDK_BUTTON_RELEASE_MASK |
OS.GDK_ENTER_NOTIFY_MASK | OS.GDK_LEAVE_NOTIFY_MASK |
OS.GDK_EXPOSURE_MASK | OS.GDK_VISIBILITY_NOTIFY_MASK |
OS.GDK_POINTER_MOTION_HINT_MASK;
attrs.window_type = OS.GDK_WINDOW_CHILD;
attrs.visual = gdkvisual;
glWindow = OS.gdk_window_new (window, attrs, OS.GDK_WA_VISUAL);
OS.gdk_window_set_user_data (glWindow, handle);
if ((style & SWT.NO_BACKGROUND) != 0) OS.gdk_window_set_back_pixmap (window, 0, false);
xWindow = OS.gdk_x11_drawable_get_xid (glWindow);
OS.gdk_window_show (glWindow);

Listener listener = new Listener () {
public void handleEvent (Event event) {
switch (event.type) {
case SWT.Paint:
/**
* Bug in MESA.  MESA does some nasty sort of polling to try
* and ensure that their buffer sizes match the current X state.
* This state can be updated using glViewport().
* FIXME: There has to be a better way of doing this.
*/
int [] viewport = new int [4];
GLX.glGetIntegerv (GLX.GL_VIEWPORT, viewport);
GLX.glViewport (viewport [0],viewport [1],viewport [2],viewport [3]);
break;
case SWT.Resize:
Rectangle clientArea = getClientArea();
OS.gdk_window_move (glWindow, clientArea.x, clientArea.y);
OS.gdk_window_resize (glWindow, clientArea.width, clientArea.height);
break;
case SWT.Dispose:
int /*long*/ window = OS.GTK_WIDGET_WINDOW (handle);
int /*long*/ xDisplay = OS.gdk_x11_drawable_get_xdisplay (window);
if (context != 0) {
if (GLX.glXGetCurrentContext () == context) {
GLX.glXMakeCurrent (xDisplay, 0, 0);
}
GLX.glXDestroyContext (xDisplay, context);
context = 0;
}
if (glWindow != 0) {
OS.gdk_window_destroy (glWindow);
glWindow = 0;
}
break;
}
}
};
addListener (SWT.Resize, listener);
addListener (SWT.Paint, listener);
addListener (SWT.Dispose, listener);
}

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