pbuffers shouldn't flip

panda/src/display/graphicsOutput.cxx

@@ -392,8 +392,7 @@ get_screenshot(PNMImage &image) {
                 PixelBuffer::F_rgb);
 
   DisplayRegion dr(_x_size, _y_size);
-  RenderBuffer rb = _gsg->get_render_buffer(RenderBuffer::T_front);
-  if (!p.copy(_gsg, &dr, rb)) {
+  if (!p.copy(_gsg, &dr, get_screenshot_buffer())) {
     return false;
   }
 
@@ -630,6 +629,19 @@ declare_channel(int index, GraphicsChannel *chan) {
   _channels[index] = chan;
 }
 
+////////////////////////////////////////////////////////////////////
+//     Function: GraphicsOutput::get_screenshot_buffer
+//       Access: Protected, Virtual
+//  Description: Returns the RenderBuffer that should be used for
+//               capturing screenshots from this particular
+//               GraphicsOutput.
+////////////////////////////////////////////////////////////////////
+RenderBuffer GraphicsOutput::
+get_screenshot_buffer() {
+  // By default, this is the front buffer.
+  return _gsg->get_render_buffer(RenderBuffer::T_front);
+}
+
 ////////////////////////////////////////////////////////////////////
 //     Function: GraphicsOutput::do_determine_display_regions
 //       Access: Private

panda/src/display/graphicsOutput.h

@@ -26,6 +26,7 @@
 #include "displayRegion.h"
 #include "graphicsStateGuardian.h"
 #include "clearableRegion.h"
+#include "renderBuffer.h"
 
 #include "typedWritableReferenceCount.h"
 #include "pStatCollector.h"
@@ -129,6 +130,7 @@ public:
 
 protected:
   void declare_channel(int index, GraphicsChannel *chan);
+  virtual RenderBuffer get_screenshot_buffer();
   
 protected:
   PT(GraphicsStateGuardian) _gsg;

panda/src/glxdisplay/glxGraphicsBuffer.cxx

@@ -91,34 +91,21 @@ release_gsg() {
 }
 
 ////////////////////////////////////////////////////////////////////
-//     Function: glxGraphicsBuffer::begin_flip
+//     Function: glxGraphicsBuffer::end_frame
 //       Access: Public, Virtual
 //  Description: This function will be called within the draw thread
-//               after end_frame() has been called on all windows, to
-//               initiate the exchange of the front and back buffers.
-//
-//               This should instruct the window to prepare for the
-//               flip at the next video sync, but it should not wait.
-//
-//               We have the two separate functions, begin_flip() and
-//               end_flip(), to make it easier to flip all of the
-//               windows at the same time.
+//               after rendering is completed for a given frame.  It
+//               should do whatever finalization is required.
 ////////////////////////////////////////////////////////////////////
 void glxGraphicsBuffer::
-begin_flip() {
-  if (_gsg != (GraphicsStateGuardian *)NULL) {
-    make_current();
-
-    if (has_texture()) {
-      // Use glCopyTexImage2D to copy the framebuffer to the texture.
-      // This appears to be the only way to "render to a texture" in
-      // OpenGL; there's no interface to make the offscreen buffer
-      // itself be a texture.
-      DisplayRegion dr(_x_size, _y_size);
-      get_texture()->copy(_gsg, &dr, _gsg->get_render_buffer(RenderBuffer::T_back));
-    }
-
-    glXSwapBuffers(_display, _pbuffer);
+end_frame() {
+  if (has_texture()) {
+    // Use glCopyTexImage2D to copy the framebuffer to the texture.
+    // This appears to be the only way to "render to a texture" in
+    // OpenGL; there's no interface to make the offscreen buffer
+    // itself be a texture.
+    DisplayRegion dr(_x_size, _y_size);
+    get_texture()->copy(_gsg, &dr, _gsg->get_render_buffer(RenderBuffer::T_back));
   }
 }
 
@@ -186,3 +173,17 @@ open_buffer() {
   _is_valid = true;
   return true;
 }
+
+////////////////////////////////////////////////////////////////////
+//     Function: glxGraphicsBuffer::get_screenshot_buffer
+//       Access: Protected, Virtual
+//  Description: Returns the RenderBuffer that should be used for
+//               capturing screenshots from this particular
+//               GraphicsOutput.
+////////////////////////////////////////////////////////////////////
+RenderBuffer glxGraphicsBuffer::
+get_screenshot_buffer() {
+  // Since the pbuffer never gets flipped, we get screenshots from the
+  // back buffer only.
+  return _gsg->get_render_buffer(RenderBuffer::T_back);
+}

panda/src/glxdisplay/glxGraphicsBuffer.h

@@ -39,12 +39,14 @@ public:
   virtual void make_current();
   virtual void release_gsg();
 
-  virtual void begin_flip();
+  virtual void end_frame();
 
 protected:
   virtual void close_buffer();
   virtual bool open_buffer();
 
+  virtual RenderBuffer get_screenshot_buffer();
+
 private:
   Display *_display;
   GLXPbuffer _pbuffer;