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# NeHe Productions: OpenGL Lesson #18

Date de publication : 31/03/2006 , Date de mise à jour : 31/03/2006

Quadrics are a way of drawing complex objects that would usually take a few FOR loops and some background in trigonometry.

We'll be using the code from lesson seven. We will add 7 variables and modify the texture to add some variety :)
 ```#include // Header File For Windows #include // Header File For Standard Input/Output #include // Header File For The OpenGL32 Library #include // Header File For The GLu32 Library #include // Header File For The GLaux Library HDC hDC=NULL; // Private GDI Device Context HGLRC hRC=NULL; // Permanent Rendering Context HWND hWnd=NULL; // Holds Our Window Handle HINSTANCE hInstance; // Holds The Instance Of The Application bool keys; // Array Used For The Keyboard Routine bool active=TRUE; // Window Active Flag Set To TRUE By Default bool fullscreen=TRUE; // Fullscreen Flag Set To Fullscreen Mode By Default bool light; // Lighting ON/OFF bool lp; // L Pressed? bool fp; // F Pressed? bool sp; // Spacebar Pressed? ( NEW ) int part1; // Start Of Disc ( NEW ) int part2; // End Of Disc ( NEW ) int p1=0; // Increase 1 ( NEW ) int p2=1; // Increase 2 ( NEW ) GLfloat xrot; // X Rotation GLfloat yrot; // Y Rotation GLfloat xspeed; // X Rotation Speed GLfloat yspeed; // Y Rotation Speed GLfloat z=-5.0f; // Depth Into The Screen GLUquadricObj *quadratic; // Storage For Our Quadratic Objects ( NEW ) GLfloat LightAmbient[]= { 0.5f, 0.5f, 0.5f, 1.0f }; // Ambient Light Values GLfloat LightDiffuse[]= { 1.0f, 1.0f, 1.0f, 1.0f }; // Diffuse Light Values GLfloat LightPosition[]= { 0.0f, 0.0f, 2.0f, 1.0f }; // Light Position GLuint filter; // Which Filter To Use GLuint texture; // Storage for 3 textures GLuint object=0; // Which Object To Draw ( NEW ) LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM); // Declaration For WndProc```
Okay now move down to InitGL(), We're going to add 3 lines of code here to initialize our quadratic. Add these 3 lines after you enable light1 but before you return true. The first line of code initializes the Quadratic and creates a pointer to where it will be held in memory. If it can't be created it returns 0. The second line of code creates smooth normals on the quadratic so lighting will look great. Other possible values are GLU_NONE, and GLU_FLAT. Last we enable texture mapping on our quadratic. Texture mapping is kind of awkward and never goes the way you planned as you can tell from the crate texture.
 ``` quadratic=gluNewQuadric(); // Create A Pointer To The Quadric Object ( NEW ) gluQuadricNormals(quadratic, GLU_SMOOTH); // Create Smooth Normals ( NEW ) gluQuadricTexture(quadratic, GL_TRUE); // Create Texture Coords ( NEW )```
Now I decided to keep the cube in this tutorial so you can see how the textures are mapped onto the quadratic object. I decided to move the cube into its own function so when we write the draw function it will appear more clean. Everybody should recognize this code. =P
 ```GLvoid glDrawCube() // Draw A Cube { glBegin(GL_QUADS); // Start Drawing Quads // Front Face glNormal3f( 0.0f, 0.0f, 1.0f); // Normal Facing Forward glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 1.0f); // Bottom Left Of The Texture and Quad glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, 1.0f); // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, 1.0f); // Top Right Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 1.0f); // Top Left Of The Texture and Quad // Back Face glNormal3f( 0.0f, 0.0f,-1.0f); // Normal Facing Away glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f); // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, 1.0f, -1.0f); // Top Right Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, 1.0f, -1.0f); // Top Left Of The Texture and Quad glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f); // Bottom Left Of The Texture and Quad // Top Face glNormal3f( 0.0f, 1.0f, 0.0f); // Normal Facing Up glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, -1.0f); // Top Left Of The Texture and Quad glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, 1.0f, 1.0f); // Bottom Left Of The Texture and Quad glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, 1.0f, 1.0f); // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, -1.0f); // Top Right Of The Texture and Quad // Bottom Face glNormal3f( 0.0f,-1.0f, 0.0f); // Normal Facing Down glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, -1.0f, -1.0f); // Top Right Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, -1.0f, -1.0f); // Top Left Of The Texture and Quad glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, 1.0f); // Bottom Left Of The Texture and Quad glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 1.0f); // Bottom Right Of The Texture and Quad // Right face glNormal3f( 1.0f, 0.0f, 0.0f); // Normal Facing Right glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f); // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, -1.0f); // Top Right Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, 1.0f, 1.0f); // Top Left Of The Texture and Quad glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, 1.0f); // Bottom Left Of The Texture and Quad // Left Face glNormal3f(-1.0f, 0.0f, 0.0f); // Normal Facing Left glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f); // Bottom Left Of The Texture and Quad glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 1.0f); // Bottom Right Of The Texture and Quad glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 1.0f); // Top Right Of The Texture and Quad glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, -1.0f); // Top Left Of The Texture and Quad glEnd(); // Done Drawing Quads }```
Next is the DrawGLScene function, here I just wrote a simple if statement to draw the different objects. Also I used a static variable (a local variable that keeps its value everytime it is called) for a cool effect when drawing the partial disk. I'm going to rewrite the whole DrawGLScene function for clarity.

You'll notice that when I talk about the parameters being used I ignore the actual first parameter (quadratic). This parameter is used for all the objects we draw aside from the cube, so I ignore it when I talk about the parameters.
 ```int DrawGLScene(GLvoid) // Here's Where We Do All The Drawing { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear The Screen And The Depth Buffer glLoadIdentity(); // Reset The View glTranslatef(0.0f,0.0f,z); // Translate Into The Screen glRotatef(xrot,1.0f,0.0f,0.0f); // Rotate On The X Axis glRotatef(yrot,0.0f,1.0f,0.0f); // Rotate On The Y Axis glBindTexture(GL_TEXTURE_2D, texture[filter]); // Select A Filtered Texture // This Section Of Code Is New ( NEW ) switch(object) // Check object To Find Out What To Draw { case 0: // Drawing Object 1 glDrawCube(); // Draw Our Cube break; // Done```
The second object we create is going to be a Cylinder. The first parameter (1.0f) is the radius of the cylinder at base (bottom). The second parameter (1.0f) is the radius of the cylinder at the top. The third parameter ( 3.0f) is the height of the cylinder (how long it is). The fouth parameter (32) is how many subdivisions there are "around" the Z axis, and finally, the fifth parameter (32) is the amount of subdivisions "along" the Z axis. The more subdivisions there are the more detailed the object is. By increase the amount of subdivisions you add more polygons to the object. So you end up sacrificing speed for quality. Most of the time it's easy to find a happy medium.
 ``` case 1: // Drawing Object 2 glTranslatef(0.0f,0.0f,-1.5f); // Center The Cylinder gluCylinder(quadratic,1.0f,1.0f,3.0f,32,32); // Draw Our Cylinder break; // Done```
The third object we create will be a CD shaped disc. The first parameter (0.5f) is the inner radius of the disk. This value can be zero, meaning there will be no hole in the middle. The larger the inner radius is, the bigger the hole in the middle of the disc will be. The second parameter (1.5f) is the outer radius. This value should be larger than the inner radius. If you make this value a little bit larger than the inner radius you will end up with a thing ring. If you make this value alot larger than the inner radius you will end up with a thick ring. The third parameter (32) is the number of slices that make up the disc. Think of slices like the slices in a pizza. The more slices you have, the smoother the outer edge of the disc will be. Finally the fourth parameter (32) is the number of rings that make up the disc. The rings are are similar to the tracks on a record. Circles inside circles. These ring subdivide the disc from the inner radius to the outer radius, adding more detail. Again, the more subdivisions there are, the slow it will run.
 ``` case 2: // Drawing Object 3 gluDisk(quadratic,0.5f,1.5f,32,32); // Draw A Disc (CD Shape) break; // Done```
Our fourth object is an object that I know many of you have been dying to figure out. The Sphere! This one is quite simple. The first parameter is the radius of the sphere. In case you're not familiar with radius/diameter, etc, the radius is the distance from the center of the object to the outside of the object. In this case our radius is 1.3f. Next we have our subdivision "around" the Z axis (32), and our subdivision "along" the Z axis (32). The more subdivisions you have the smoother the sphere will look. Spheres usually require quite a few subdivisions to make them look smooth.
 ``` case 3: // Drawing Object 4 gluSphere(quadratic,1.3f,32,32); // Draw A Sphere break; // Done```
Our fifth object is created using the same command that we used to create a Cylinder. If you remember, when we were creating the Cylinder the first two parameters controlled the radius of the cylinder at the bottom and the top. To make a cone it makes sense that all we'd have to do is make the radius at one end Zero. This will create a point at one end. So in the code below, we make the radius at the top of the cylinder equal zero. This creates our point, which also creates our cone.
 ``` case 4: // Drawing Object 5 glTranslatef(0.0f,0.0f,-1.5f); // Center The Cone gluCylinder(quadratic,1.0f,0.0f,3.0f,32,32); // A Cone With A Bottom Radius Of .5 And A Height Of 2 break; // Done```
Our sixth object is created with gluPartialDisc. The object we create using this command will look exactly like the disc we created above, but with the command gluPartialDisk there are two new parameters. The fifth parameter (part1) is the start angle we want to start drawing the disc at. The sixth parameter is the sweep angle. The sweep angle is the distance we travel from the current angle. We'll increase the sweep angle, which causes the disc to be slowly drawn to the screen in a clockwise direction. Once our sweep hits 360 degrees we start to increase the start angle. the makes it appear as if the disc is being erased, then we start all over again!
 ``` case 5: // Drawing Object 6 part1+=p1; // Increase Start Angle part2+=p2; // Increase Sweep Angle if(part1>359) // 360 Degrees { p1=0; // Stop Increasing Start Angle part1=0; // Set Start Angle To Zero p2=1; // Start Increasing Sweep Angle part2=0; // Start Sweep Angle At Zero } if(part2>359) // 360 Degrees { p1=1; // Start Increasing Start Angle p2=0; // Stop Increasing Sweep Angle } gluPartialDisk(quadratic,0.5f,1.5f,32,32,part1,part2-part1); // A Disk Like The One Before break; // Done }; xrot+=xspeed; // Increase Rotation On X Axis yrot+=yspeed; // Increase Rotation On Y Axis return TRUE; // Keep Going }```
In the KillGLWindow() section of code, we need to delete the quadratic to free up system resources. We do this with the command gluDeleteQuadratic.
 ```GLvoid KillGLWindow(GLvoid) // Properly Kill The Window { gluDeleteQuadric(quadratic); // Delete Quadratic - Free Resources```
Now for the final part, they key input. Just add this where we check the rest of key input.
 ``` if (keys[' '] && !sp) // Is Spacebar Being Pressed? { sp=TRUE; // If So, Set sp To TRUE object++; // Cycle Through The Objects if(object>5) // Is object Greater Than 5? object=0; // If So, Set To Zero } if (!keys[' ']) // Has The Spacebar Been Released? { sp=FALSE; // If So, Set sp To FALSE }```
Thats all! Now you can draw quadrics in OpenGL. Some really impressive things can be done with morphing and quadrics. The animated disc is an example of simple morphing.

Everyone if you have time go check out my website, TipTup.Com 2000 .

GB Schmick ( TipTup )

Jeff Molofee ( NeHe )

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