Archived

This topic is now archived and is closed to further replies.

SneakyTommy

Left is right?

Recommended Posts

Here''s the situation that I don''t understand. I''m trying to draw a spinning triangle on the left, a square on the right (exactly like on Nehe''s lesson 3) But, when I port the code onto my MFC child window, I get the triangle on the right, square on the left. The y and z axis are both correct. It''s just seems the x-axis is flipped around. All the code is for the OpenGL bit is the same as from Nehe''s lesson 3, so I don''t understand what''s wrong... void CGlView::vDrawGLScene() { static GLfloat rtri; static GLfloat rquad; glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear Screen And Depth Buffer glLoadIdentity(); // Reset The Current Modelview Matrix glTranslatef(-1.5f,0.0f,-6.0f); // Move Left 1.5 Units And Into The Screen 6.0 glRotatef(rtri,0.0f,0.1f,0.0f); // Rotate The Triangle On The Y axis ( NEW ) glBegin(GL_TRIANGLES); // Start Drawing A Triangle glColor3f(1.0f,0.0f,0.0f); // Set Top Point Of Triangle To Red glVertex3f( 0.0f, 1.0f, 0.0f); // First Point Of The Triangle glColor3f(0.0f,1.0f,0.0f); // Set Left Point Of Triangle To Green glVertex3f(-1.0f,-1.0f, 0.0f); // Second Point Of The Triangle glColor3f(0.0f,0.0f,1.0f); // Set Right Point Of Triangle To Blue glVertex3f( 1.0f,-1.0f, 0.0f); // Third Point Of The Triangle glEnd(); // Done Drawing The Triangle glLoadIdentity(); // Reset The Current Modelview Matrix glTranslatef(1.5f,0.0f,-6.0f); // Move Right 1.5 Units And Into The Screen 6.0 glRotatef(rquad,1.0f,0.0f,0.0f); // Rotate The Quad On The X axis ( NEW ) glColor3f(0.5f,0.5f,1.0f); // Set The Color To Blue One Time Only glBegin(GL_QUADS); // Draw A Quad glVertex3f(-1.0f, 1.0f, 0.0f); // Top Left glVertex3f( 1.0f, 1.0f, 0.0f); // Top Right glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left glEnd(); // Done Drawing The Quad rtri+=1.2f; // Increase The Rotation Variable For The Triangle ( NEW ) rquad-=1.15f; // Decrease The Rotation Variable For The Quad ( NEW ) // swap the buffer SwapBuffers(m_hDC); } CGlView::CGlView(CWnd *pclWnd) { m_pclWnd = pclWnd; m_hDC = ::GetDC(pclWnd->m_hWnd); // Get Handle of Static Box BOOL bSuccess; RECT rect; m_pclWnd->GetClientRect(&rect); // Get dimensions of box int iWidth = rect.right - rect.left; int iHeight = rect.top - rect.bottom; bSuccess = bSetWindowPixelFormat(m_hDC); // Set Pixel Format in that box ASSERT(&bSuccess); bSuccess = bCreateViewGLContext(m_hDC); // Create a OpenGL view in Box ASSERT(&bSuccess); vInitGl(iWidth, iHeight); // Call our initialization routine g_pclGLView = this; } void CGlView::vInitGl(int iWidth, int iHeigth) { glShadeModel(GL_SMOOTH); // Enable Smooth Shading glClearColor(0.0f, 0.0f, 0.0f, 0.5f); // Black Background glClearDepth(1.0f); // Depth Buffer Setup glEnable(GL_DEPTH_TEST); // Enables Depth Testing glDepthFunc(GL_LEQUAL); // The Type Of Depth Testing To Do glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); // Really Nice Perspective Calculations glViewport(0,0,iWidth,iHeigth); // Reset The Current Viewport glMatrixMode(GL_PROJECTION); // Select The Projection Matrix glLoadIdentity(); // Reset The Projection Matrix // Calculate The Aspect Ratio Of The Window gluPerspective(45.0f,(GLfloat)iWidth/(GLfloat)iHeigth,0.1f,100.0f); glMatrixMode(GL_MODELVIEW); // Select The Modelview Matrix glLoadIdentity(); // Reset The Modelview Matrix }

Share this post


Link to post
Share on other sites
Try using the matrix stacks with glPushMatrix() and glPopMatrix(). Try it like this:

// Push scene into view
glTranslatef( 0.0f, 0.0f, -6.0f );

glPushMatrix();
glRotatef(blah);
DrawShape1();
glPopMatrix();

glPushMatrix();
glRotatef(blah);
DrawShape();
glPopMatrix();

IncrementRotation();

SwapBuffers();

-SirKnight

Share this post


Link to post
Share on other sites
Thanks for replying, but unfortunately, I tried what you suggested (Push/Pop) and it didn''t work. The x-axis is still flipped. (triangle on right, square on left)

you can test this by downloading this source code from OpenGL''s website:

http://www.opengl.org/developers/faqs/technical/mswindows.htm#mswi0160

and then paste this little code from NeHe''s Lesson 4

//====================================================
void CGlView::vDrawGLScene()
{

static GLfloat rtri;
static GLfloat rquad;

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glTranslatef(-1.5f,0.0f,-6.0f); //<--- should move left
glRotatef(rtri,0.0f,0.1f,0.0f);
glBegin(GL_TRIANGLES);
glColor3f(1.0f,0.0f,0.0f);
glVertex3f( 0.0f, 1.0f, 0.0f);
glColor3f(0.0f,1.0f,0.0f);
glVertex3f(-1.0f,-1.0f, 0.0f);
glColor3f(0.0f,0.0f,1.0f);
glVertex3f( 1.0f,-1.0f, 0.0f);
glEnd();
glTranslatef(3.0f,0.0f,0.0f); // //<--- should move right
glRotatef(rquad,1.0f,0.0f,0.0f);
glColor3f(0.5f,0.5f,1.0f);
glBegin(GL_QUADS);
glVertex3f(-1.0f, 1.0f, 0.0f);
glVertex3f( 1.0f, 1.0f, 0.0f);
glVertex3f( 1.0f,-1.0f, 0.0f);
glVertex3f(-1.0f,-1.0f, 0.0f);
glEnd();
rtri+=1.2f;
rquad-=1.15f;

// swap the buffer
SwapBuffers(m_hDC);
}

//====================================================

I also discovered a couple things. If you run their program under "release" mode instead if "debug" mode, all the colors disappear and shows an ugly red. But if you close and run it again immediately, sometimes the color will show up again. VERY strange.

Can anyone solve this problem or is MFC+OpenGL doomed?

Share this post


Link to post
Share on other sites
A bit of a strange suggestion, maybe, but try adding glMatrixMode (GL_MODELVIEW) to the start of your scene drawing code.

Also, check whether iWidth is actually positive.

It might not do any good because of what you describe as happening in a release build. Stuff like that is usually indicative of members not being initialised correctly (although I don''t see any of that in your program) or writing at an incorrect location in memory (apparently without triggering a GPF).

Oh, and you should also make sure that the window has the WS_CLIPCHILDREN and WS_CLIPSIBLINGS and that the window class has CS_OWNDC set.

Share this post


Link to post
Share on other sites
Well, Kippesoep, you are now officially my hero of the day.

It wasn''t the GL_MODELVIEW or iWidth that was messed up. However, while checking iWidth, I noticed iHeight was negative. Fixing it and making it positive did the job. I''m not really sure why the height affects the x-axis, but anyway, it''s working.

Now, my only problem is that the release version doesn''t show color when running most of the time (run 5 times, 1 will show the correct color). However, I noticed something that might be an important clue. Running on two of my desktop computers with TNT2 3D cards will results the above situation. But, if I run it on my notebook that has no 3D graphics card, it shows the correct colors 100% everytime I it (but turning really slow, of course). Could it be some OpenGL init routine might be skipped or something?

Share this post


Link to post
Share on other sites
I''ll bet your negative height contributed to the problem because you''re using iHeight in your call to gluPerspective().

Share this post


Link to post
Share on other sites