CODEWITHSUNDEEP
opengljogl
Andrii Andriichuk
Andrii Andriichuk

Reputation: 663

opengl don't call glClear() in render

I draw GLUT primitives each render, more and more. To make things faster, I decided not to clear every time, just put new primitives. Is that just wrong?

When I did this, I got blinking. Putting sleep() showed that one frame is ok and second is empty and so on.

EDIT: Brief code in render(display) that is executed once(I use Java's JOGL):

gl.glPushMatrix(); 
gl.glColor3f(1, 1, 0);
gl.glTranslatef(0, 0, 0);
glut.glutSolidCube(10);
gl.glPopMatrix();
drawable.swapBuffers();

Upvotes: 0

Views: 2019

Answers (3)

Michael IV
Michael IV

Reputation: 11506

Sure it is empty.When you clear, you clear the front buffer frame.Then , when swapBuffers() called the back-buffer frame becomes front , and in the meanwhile your stuff is being drawn to the front buffer frame ,which just has become back-buffer frame.Then ,when the backbuffer frame is finished the buffer swap is done(triggered by the call to swapBuffers().That is how double buffering works.If you don't clear the frame color you will get your drawings accumulated in the front buffer over time ,which I am not sure is desired result. Clearing the front buffer once in the beginning of every render loop is not a big performance hit.The problem appears when you call glClear() frequently ,like calling it before each object drawing which also doesn't make sense as in such a case you will see only the last drawn object. For the flickering - you should be more descriptive on how you do it all.From your example it is unclear why it happens.

Upvotes: 1

Kevin
Kevin

Reputation: 2730

Swapbuffers(HDC) doesn't actually copy the contents of the buffer but merely swaps the front and back buffer, that is why you see every odd frame, but not the even ones.

Upvotes: 0

JohnD
JohnD

Reputation: 1159

gl.glDisable(GL_DEPTH_TEST);

?

It's hard to say without seeing more of your code.

When ever I get unexpected results in openGL code, I mentally go through the list of state possibilities and set them either enabled or disabled:

  • Depth Test
  • Texturing
  • Lighting
  • Blending
  • Culling
  • Framebuffers
  • Shaders

Upvotes: 0

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