I'm working with some OpenGL code for scientific visualization and I'm having issues getting its rubber banding working on newer hardware. The code is drawing a "Zoom Window" over an existing scene with one corner of the "Zoom Window" at the stored left-click location, and the other under the mouse as it is moved. On the second left-click the scene zooms into the selected window.
The symptoms I am seeing as the mouse is moved across the scene are:
The above problem doesn't happen on low end hardware such as the integrated graphics on a netbook I have. Also, I can't recall this problem ~5 years ago when this code was written.
Here are the relevant code sections, trimmed down to focus on the relevant OpenGL:
// Called by every mouse move event
// Makes use of current device context (m_hDC) and rendering context (m_hRC)
void MyViewClass::DrawLogic()
{
BOOL bSwapRv = FALSE;
// Make the rendering context current
if (!wglMakeCurrent(m_hDC, m_hRC))
// ... error handling
// Perform the logic rendering
glLogicOp(GL_XOR);
glEnable(GL_COLOR_LOGIC_OP);
// Draws the rectangle on the buffer using XOR op
RenderLogic();
bSwapRv = ::SwapBuffers(m_hDC);
// Removes the rectangle from the buffer via a second pass
RenderLogic();
glDisable(GL_COLOR_LOGIC_OP);
// Release the rendering context
if (!wglMakeCurrent(NULL, NULL))
// ... error handling
}
void MyViewClass::RenderLogic(void)
{
glLineWidth(1.0f);
glColor3f(0.6f,0.6f,0.6f);
glEnable(GL_LINE_STIPPLE);
glLineStipple(1, 0x0F0F);
glBegin(GL_LINE_LOOP);
// Uses custom "Point" class with Coords() method returning double*
// Draw rectangle with corners at clicked location and current location
glVertex2dv(m_pntClickLoc.Coords());
glVertex2d(m_pntCurrLoc.X(), m_pntClickLoc.Y());
glVertex2dv(m_pntCurrLoc.Coords());
glVertex2d(m_pntClickLoc.X(), m_pntCurrLoc.Y());
glEnd();
glDisable(GL_LINE_STIPPLE);
}
// Setup code that might be relevant to the buffer configuration
bool MyViewClass::SetupPixelFormat()
{
PIXELFORMATDESCRIPTOR pfd = {
sizeof(PIXELFORMATDESCRIPTOR),
1, // Version number (?)
PFD_DRAW_TO_WINDOW // Format must support window
| PFD_SUPPORT_OPENGL // Format must support OpenGL
| PFD_DOUBLEBUFFER, // Must support double buffering
PFD_TYPE_RGBA, // Request an RGBA format
32, // Select a 32 bit colour depth
0, 0, 0, 0, 0, 0, // Colour bits ignored (?)
8, // Alpha buffer bits
0, // Shift bit ignored (?)
0, // No accumulation buffer
0, 0, 0, 0, // Accumulation bits ignored
16, // 16 bit Z-buffer
0, // No stencil buffer
0, // No accumulation buffer (?)
PFD_MAIN_PLANE, // Main drawing layer
0, // Number of overlay and underlay planes
0, 0, 0 // Layer masks ignored (?)
};
PIXELFORMATDESCRIPTOR chosen_pfd;
memset(&chosen_pfd, 0, sizeof(PIXELFORMATDESCRIPTOR));
chosen_pfd.nSize = sizeof(PIXELFORMATDESCRIPTOR);
// Find the closest match to the pixel format
m_uPixelFormat = ::ChoosePixelFormat(m_hDC, &pfd);
// Make sure a pixel format could be found
if (!m_uPixelFormat)
return false;
::DescribePixelFormat(m_hDC, m_uPixelFormat, sizeof(PIXELFORMATDESCRIPTOR), &chosen_pfd);
// Set the pixel format for the view
::SetPixelFormat(m_hDC, m_uPixelFormat, &chosen_pfd);
return true;
}
Any pointers on how to remove the artefacts will be much appreciated.
@Krom - image below
With OpenGL it's canonical to redraw the whole viewport if just anything changes. Consider this: Modern system draw animates complex scenes at well over 30 FPS.
But I understand, that you may want to avoid this. So the usual approach is to first copy the frontbuffer in a texture, before drawing the first rubberband. Then for each rubberband redraw "reset" the image by drawing a framebuffer filling quad with the texture.