I'm trying to draw 2 squares side by side of different colours, my problem is I can't get glTranslatef to move my second square to the right, the second square just draws over the first.
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPointSize(10);
glBegin(GL_QUADS);
glColor3f(0.0,1.0,0.0);
drawSquare();
glTranslatef(10,0,0);
glColor3f(1.0,0.0,0.0);
drawSquare();
glEnd();
glFlush(); // Process all OpenGL routines
}
void drawSquare()
{
glVertex3f(0,0,0);
glVertex3f(10,0,0);
glVertex3f(10,10,0);
glVertex3f(0,10,0);
}
You cannot translate inside a glBegin/glEnd block, you have break it up into two blocks.
I recommend to start using glGetError() in your code, it will help you find mistakes like this.
Only a certain subset of OpenGL commands is allowed between glBegin and glEnd. So, when you call glTranslate between those two calls, it is ignored.
Remove glBegin and glEnd from display, and put in drawSquare - that should work.
Related
I am currently working on the printing loop of my software that reads 3D obj file.
I have stored my obj file read in the variable tie. This variable contain an OpenGL list. My objective is to be able to move around the read object by using keyboard. The keyboard reading is implemented correctly (i can see in through the logs).
Issue
When i compile the following code loop, the gluLookAt exucute properly and I am able to move around my object by changing the value of the parameters.
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT) ;
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
light();
gluPerspective (60.0, 250/(float)250, 0.1, 500.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(eyeX,eyeY,eyeZ,eyeX+directionX,eyeY+directionY,eyeZ+directionZ,upX,upY,upZ);
glPushMatrix();
glRotated(45,0,0,1);
glTranslated(0,0,50);
glBindTexture(GL_TEXTURE_2D,texture1);
//glCallList(xwing); //ICI
glEnd();
glPopMatrix();
glColor3d(1,1,1);
glDisable(GL_LIGHTING);
glBindTexture(GL_TEXTURE_2D,texture2);
GLUquadric* params = gluNewQuadric();
gluQuadricDrawStyle(params,GLU_FILL);
gluQuadricTexture(params,GL_TRUE);
gluSphere(params,100,20,20);
gluDeleteQuadric(params);
glEnable(GL_LIGHTING);
glBindTexture(GL_TEXTURE_2D,texture1);
glCallList(tie); //ICI
glPointSize(5.0);
glBegin(GL_POINTS);
glColor3f(1.0f,0.0f,0.0f);
glVertex3f(-1.0f,0.0f,0.0f);
glEnd();
SwapBuffers(hDC);
//} //else
Sleep(1);
But when i comment these 4 lines:
glBegin(GL_POINTS);
glColor3f(1.0f,0.0f,0.0f);
glVertex3f(-1.0f,0.0f,0.0f);
glEnd();
My object doesn't move anymore. As if gluLookAt didn't succeed to execute.
Do you have any idea why is this happening. Did I forget something in my code?
glBegin and glEnd delimit the vertices that define a primitive or a group of like primitives. You have to ensure, the each glBegin is followed by a glEnd.
This means, if your Display Lists contains a glBegin then it should contain a glEnd, too. I strongly recommend to do it this way. The other possibility would be to do it manually after glCallList:
glCallList(tie);
glEnd();
glPushMatrix and glPopMatrix are used to push matrices on and pop matrices from the matrix stack. If you want to add a model matrix to the view matrix, then you have to do the following steps.
Push the view matrix glPushMatrix. This pushs a copy of the view matrix on the stack.
Add the model matrix to the current view matrix (glRotated, glTranslated, ... )
Draw the model. (glCallList, gluSphere, ... )
Restore the original view matrix (glPopMatrix).
Adapt your code somehow like this:
// set up view matrix
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(eyeX,eyeY,eyeZ,eyeX+directionX,eyeY+directionY,eyeZ+directionZ,upX,upY,upZ);
// save view matrix
glPushMatrix();
// add model matrix
glRotated(45,0,0,1);
glTranslated(0,0,50);
// do the drawing
glColor3d(1,1,1);
glDisable(GL_LIGHTING);
glBindTexture(GL_TEXTURE_2D,texture2);
GLUquadric* params = gluNewQuadric();
gluQuadricDrawStyle(params,GLU_FILL);
gluQuadricTexture(params,GL_TRUE);
gluSphere(params,100,20,20);
gluDeleteQuadric(params);
glEnable(GL_LIGHTING);
glBindTexture(GL_TEXTURE_2D,texture1);
glCallList(tie);
glEnd(); // <-- maybe this could be done in "tie"
// restore the view matrix
glPopMatrix();
So, I've been trying to rotate a single object in an OpenGL/GLUT environment.
After going through several questions on SO and the like, I've written what appears to be correct code, but no dice. Does anyone know how to make this work?
PS: I've tried changing the GLMatrixmode to Projection, but that just shows a black screen. Same thing happens if I use glLoadIdentity().
Here's my rendering code
void display()
{
preProcessEvents();
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
gluLookAt(Camera::position.x, Camera::position.y, Camera::position.z,
Camera::position.x+Math::sind(Camera::rotationAngles.x)*Math::cosd(Camera::rotationAngles.y),
Camera::position.y+Math::cosd(Camera::rotationAngles.x),
Camera::position.z+Math::sind(Camera::rotationAngles.x)*Math::sind(Camera::rotationAngles.y),
0.0, 1.0, 0.0);
glBegin(GL_TRIANGLES);
glColor3f(1, 0, 0);
glVertex3f(-1, 0,-3);
glColor3f(0, 1, 0);
glVertex3f(0.0f, 2.0f,-3);
glColor3f(0, 0, 1);
glVertex3f(1.0f, 0.0f,-3);
glEnd();
glBindTexture(GL_TEXTURE_2D, tex->textureID);
glBegin(GL_QUADS);
glColor3f(1, 1, 1);
glTexCoord2f(100, 100);
glVertex3f(100,0,100);
glTexCoord2f(-100, 100);
glVertex3f(-100,0,100);
glTexCoord2f(-100,-100);
glVertex3f(-100,0,-100);
glTexCoord2f(100,-100);
glVertex3f(100,0,-100);
glEnd();
glBindTexture(GL_TEXTURE_2D, 0);
object1.draw();
glTranslatef(-10.0, 10.0, 0.0);
glBindTexture(GL_TEXTURE_2D, tex2->textureID);
gluQuadricTexture(quad,1);
gluSphere(quad,10,20,20);
glBindTexture(GL_TEXTURE_2D, 0);
//RELEVANT CODE STARTS HERE
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
glRotatef(190, 0.0, 0.0, 1.0);
glPopMatrix();
glutSwapBuffers();
}
Are you aware what glPushMatrix and glPopMatrix do? They save and restore the "current" matrix.
By enclosing your rotation in that and then doing no actual drawing operation before restoring the matrix the entire sequence of code beginning with //RELEVANT CODE STARTS HERE is completely pointless.
Even if you did not push/pop, your rotation would only be applied the next time you draw something. Logically you might think that would mean the next time you call display (...), but one of the first things you do in display (...) is replace the current matrix with an identity matrix (line 3).
In all honesty, you should consider abandoning whatever resource you are currently using to learn OpenGL. You are using deprecated functionality and missing a few fundamentals. A good OpenGL 3.0 tutorial will usually touch on the basics of transformation matrices.
As for why changing the matrix mode to projection produces a black screen, that is because the next time you call display (...), gluLookAt operates on the projection matrix. In effect, you wind up applying the camera transformation twice. You should really add glMatrixMode (GL_MODELVIEW) to the beginning of display (...) to avoid this.
You do the rotation (and reset it with glPopMatrix) after you draw, do the rotation code before the glBegin/glEnd calls.
Or just move to the shader based pipeline and manage you own transformation matrices.
In my openGL program using freeglut the screen is completely whited out by this code:
glBegin(GL_QUADS);
glPushMatrix();
glVertex3f(trackRadius*cos((double)x), trackHeight*sin(trackNumberOfHills*x), trackRadius*sin(x));
glVertex3f((trackRadius+1)*cos((double)x), trackHeight*sin(trackNumberOfHills*x), (trackRadius+1)*sin(x));
glVertex3f(trackRadius*cos((double)x+(0.005)), trackHeight*sin(trackNumberOfHills*(x+0.005)), trackRadius*sin(x+0.005));
glVertex3f((trackRadius+1)*cos((double)x+0.005), trackHeight*sin(trackNumberOfHills*(x+0.005)), (trackRadius+1)*sin(x+0.005));
glPopMatrix();
glEnd();
The above code is used to display lines between two railroad tracks which are generated and displayed just fine when the above code is removed. A kart is also displayed fine.
I've discovered that if I remove glPushMatrix(); and glPopMatrix(); everything displays fine, but I need the matrix push/pop lines don't I?
Edit 1:
This is the full code I call to display my track in a class Track.cpp called from my main glut .cpp
void Track::RenderTrack()
{
double x=-3.14;
glNewList(1, GL_COMPILE); // create sphere display list for Object 1
glutSolidSphere(0.1,20,20);
glEndList();
glNewList(2, GL_COMPILE);
for (x; x<3.14;x= x+.005)
{
//first track
glPushMatrix();
glColor3f(1.0,0.0,0.0);
glTranslatef(trackRadius*cos((double)x),trackHeight * sin((double)trackNumberOfHills*x),trackRadius*sin((double)x));
glCallList(1);
glPopMatrix();
//Second track
glPushMatrix();
glColor3f(0.0,1.0,0.0);
glTranslatef((trackRadius+1)*cos(x),trackHeight * sin(trackNumberOfHills*x),(trackRadius+1)*sin(x));
glCallList(1);
glPopMatrix();
//Track Insides
glBegin(GL_QUADS);
glPushMatrix();
glVertex3f(trackRadius*cos((double)x), trackHeight*sin(trackNumberOfHills*x), trackRadius*sin(x));
glVertex3f((trackRadius+1)*cos((double)x), trackHeight*sin(trackNumberOfHills*x), (trackRadius+1)*sin(x));
glVertex3f(trackRadius*cos((double)x+(0.005)), trackHeight*sin(trackNumberOfHills*(x+0.005)), trackRadius*sin(x+0.005));
glVertex3f((trackRadius+1)*cos((double)x+0.005), trackHeight*sin(trackNumberOfHills*(x+0.005)), (trackRadius+1)*sin(x+0.005));
glPopMatrix();
glEnd();
}
glEndList();
glCallList(2); // call the list to draw it
}
From opengl documentation:
Only a subset of GL commands can be used between glBegin and glEnd. The commands are glVertex, glColor, glSecondaryColor, glIndex, glNormal, glFogCoord, glTexCoord, glMultiTexCoord, glVertexAttrib, glEvalCoord, glEvalPoint, glArrayElement, glMaterial, and glEdgeFlag. Also, it is acceptable to use glCallList or glCallLists to execute display lists that include only the preceding commands. If any other GL command is executed between glBegin and glEnd, the error flag is set and the command is ignored.
glPushMatrix and glPopMatrix are not in this list, so your code is ignored.
You can put them outside the glBegin / glEnd block.
I'm trying to use the QGLWidget to use OpenGL in a Qt application.
I made a subclass of QGLWidget etc., and thought I'd test if it works.
However, the following code is not working as I expected it would:
void MyGLWidget::paintGL() {
gluLookAt(0,0,-10,0.5,0.5,0,0,1,0);
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(1,0,0);
glBegin(GL_POLYGON);
glVertex3f(0,0,0);
glVertex3f(0,1,0);
glVertex3f(1,1,0);
glVertex3f(1,0,0);
glEnd();
}
What I imagined this would do is look at the center of a red square. But instead, when I run it, it seems to extremely briefly look at the center of the square, and then the display just becomes black.
Is there something I'm doing wrong? I'm not doing any OpenGL anywhere else. The function above is the only OpenGL code in the subclass (for now there's nothing in ::resizeGL() and ::initializeGL()).
I think you need to setup the OpenGL viewport. There are some Qt+OpenGL examples in the SDK. Take a look!
It seems that there were two problems with my code. First, I had to set up the view port in :
void MyGLWidget::resizeGL(int w, int h) {
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.,((GLfloat)w)/((GLfloat)h),0.1f,1000.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
and secondly, I had to call glLoadIdentity() before calling gluLookAt() in paintGL().
I'm working on a little example, where I have loaded an object from a wavefront file - and am trying to get my picking right, I've gone over this and a few tutorials about 10 times... but must be missing something. Was wondering if anyone could provide an extra set of eyes.
I've used a saved list to draw the object, which appears fine on the screen... At the moment, when gl_select(x, y) runs, I get a hit no matter what, and if I enable the translate/rotate code (which is currently commented out) - I get no hits what-so-ever.
Relevant code blocks:
// gl_select, is called when the mouse is clicked, with its x and y coords
void gl_select(int x, int y)
{
GLuint buff[256];
GLint hits;
GLint view[4];
//Buffer to store selection data
glSelectBuffer(256, buff);
//Viewport information
glGetIntegerv(GL_VIEWPORT, view);
//Switch to select mode
glRenderMode(GL_SELECT);
//Clear the name stack!
glInitNames();
//Fill the stack with one element
glPushName(0);
//Restric viewing volume
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
//Restrict draw area
gluPickMatrix(x, y, 1.0, 1.0, view);
gluPerspective(60, 1, 0.0001, 1000.0);
//Draw the objects onto the screen
glMatrixMode(GL_MODELVIEW);
//Draw only the names in the stack
glutSwapBuffers();
DrawSavedObject();
//Back into projection mode to push the matrix
glMatrixMode(GL_PROJECTION);
glPopMatrix();
hits = glRenderMode(GL_RENDER);
cout << hits;
//Back to modelview mode
glMatrixMode(GL_MODELVIEW);
}
And the draw functions:
void DrawSavedObject()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glColor3f(1.0,0.0,0.0);
//translate and rotate
//glRotated(rotation,0.0,0.0,1.0);
//glTranslated(7.0, 7.0, 0.0);
//Draw the saved object
glLoadName(7);
glCallList(list_object);
glutSwapBuffers();
}
And where the list is saved:
void SaveDisplayList(){
glNewList(list_object, GL_COMPILE);
glVertexPointer(3, GL_DOUBLE, 3*sizeof(GLdouble), vertices);
glEnableClientState(GL_VERTEX_ARRAY);
glDrawElements(GL_TRIANGLES, verticesSize ,GL_UNSIGNED_INT, triangles);
glDisableClientState(GL_VERTEX_ARRAY);
glEndList();
}
Sorry again for the chunkiness of the code blocks.
A few things to consider here:
OpenGL selection mode is deprecated and never was HW accelerated, except on a few SGI boxes and 3DLabs GPUs.
DisplayLists don't mix with Vertex Arrays.
Why do you call glutSwapBuffers right before drawing your list of saved objects? Makes absolutely no sense at all.
I'm not sure if it's relevant but you're not supposed to store things like glVertexPointer in display lists. From the spec http://www.opengl.org/sdk/docs/man/xhtml/glNewList.xml:
Certain commands are not compiled into the display list but are
executed immediately, regardless of the display-list mode. These
commands are glAreTexturesResident, glColorPointer, glDeleteLists,
glDeleteTextures, glDisableClientState, glEdgeFlagPointer,
glEnableClientState, glFeedbackBuffer, glFinish, glFlush, glGenLists,
glGenTextures, glIndexPointer, glInterleavedArrays, glIsEnabled,
glIsList, glIsTexture, glNormalPointer, glPopClientAttrib,
glPixelStore, glPushClientAttrib, glReadPixels, glRenderMode,
glSelectBuffer, glTexCoordPointer, glVertexPointer, and all of the
glGet commands.
This could be what's causing your problem.