Drawing trigonometric graphs with OpenGL?

Question

I am trying to draw a trigonometric graph with OpenGL. This is a part of my code:

   double x = -1;
   gl.glColor3d(0, 0, 0);
   gl.glBegin(gl.GL_LINES);
    gl.glVertex2d(x, Math.sin(Math.toRadians(x))*0.01);
    gl.glVertex2d(x+0.01, Math.sin(Math.toRadians(x+0.01))*0.01);
   gl.glEnd();

   x += 0.01;

This part is repeated in my full code. When this is executed, I see nothing. Can anybody tell me why this might be happening?

Is your background black? Is the context initialized? Can you draw tringles or anything else? — MalaKa, Apr 23 '17 at 08:45
My Background is white and the line has a black colour and the context is initialized @MalaKa — ianc1339, Apr 23 '17 at 09:30

score 0 · Accepted Answer · edited May 23 '17 at 12:09

I do not see any loop in your code

and also the scales are suspicious (without matrices hard to tell) try this instead:
```
double x;
gl.glColor3d(0.0, 0.0, 0.0);
gl.glBegin(gl.GL_LINE_STRIP);
for (x=-180.0;x<=180.0;x+=0.01)
 gl.glVertex2d(x/180.0, Math.sin(Math.toRadians(x)));
gl.glEnd();
```
it uses LINE_STRIP instead of LINES and the graph is scaled to <-1,+1> which is most likely your viewing area...
settings

Also there might be other problems like the comments suggest. On top of them check the obvious:
```
gl.glDisable(gl.GL_DEPTH_TEST);
gl.glDisable(gl.GL_TEXTURE_2D);
```
in case they has been set from other part of your code...
wrong camera settings

I do not see any matrix code so I hope your camera is facing the correct direction and your graph is inside frustrum or whatever you use...

GL rendering

In case your GL code is missing or has wrong structure then it should look like this (puted together all the bullets):

// (double) buffering
gl.glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
gl.glClear(gl.GL_COLOR_BUFFER_BIT | gl.GL_DEPTH_BUFFER_BIT); // non eed for the depth although
// here set matrices in case they are not persistent
gl.glMatrixMode(gl.GL_MODELVIEW);
gl.glLoadIdentity();
gl.glMatrixMode(gl.GL_PROJECTION);
gl.glLoadIdentity();
// here set/reset config the pipeline
gl.glDisable(gl.GL_DEPTH_TEST);
gl.glDisable(gl.GL_TEXTURE_2D);
gl.glLineWidth(1.0);
// here render
double x;
gl.glColor3d(0.0, 0.0, 0.0);
gl.glBegin(gl.GL_LINE_STRIP);
for (x=-180.0;x=<180.0;x+=0.01)
 gl.glVertex2d(x/180.0, Math.sin(Math.toRadians(x)));
gl.glEnd();
// (double) buffering
gl.glFlush();
SwapBuffers(hdc);

I do not code in JAVA so instead of SwapBuffers(hdc); use whatever you got in JAVA for the same purpose. Hope I did not make any mistake while translating to JAVA.

For more info see:

simple complete GL+VAO/VBO+GLSL+shaders example in C++

@kimchiboy03 now you can rem out line by line to find out what was the problem in the first place. My bet is your matrices was not set for the scale you was rendering or at all. — Spektre, Apr 24 '17 at 06:10

Drawing trigonometric graphs with OpenGL?

1 Answers1