glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
glLoadIdentity();
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glDepthMask(GL_FALSE);
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_ALWAYS, 1, 0xFFFFFFFF);
glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
DrawSurface();
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glDepthMask(GL_TRUE);
glStencilFunc(GL_EQUAL, 1, 0xFFFFFFFF);
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
glPushMatrix();
glScalef(1.0f, -1.0f, 1.0f);
DrawObject();
glPopMatrix();
glEnable(GL_BLEND);
DrawSurface();
glDisable(GL_BLEND);
glDisable(GL_STENCIL_TEST);
glPushMatrix();
DrawObject();
glPopMatrix();
stencil buffer
Author
I''ve been trying to use the stencil buffer to get a reflection but you can still see the object I''m trying to reflect below the surface. I don''t understand what is going wrong, I''ve followed the example in the OpenGL Game Programming book and NeHe''s tutorial, but I still can''t get it to work. Anyone know what''s going wrong in the following code? Thanks.
Well, you might try this to make it work:
disable GL_DEPTH_TEST before you draw your reflective surface (the ground) the first time. Then enable it after you draw the surface. Also, the glStencilFunc(GL_ALWAYS, 1, 1) works instead. But i think your big problem is not disabling depth testing. What happens is the reflective surface is closer than your reflected image and opengl won''t draw anything behind the surface.
disable GL_DEPTH_TEST before you draw your reflective surface (the ground) the first time. Then enable it after you draw the surface. Also, the glStencilFunc(GL_ALWAYS, 1, 1) works instead. But i think your big problem is not disabling depth testing. What happens is the reflective surface is closer than your reflected image and opengl won''t draw anything behind the surface.
Author
That''s why I don''t understand why it won''t work, because I tried disabling depth testing with glDisable(GL_DEPTH_TEST). Here''s the part of the code where I disable all the things including the glDisable calls:
Am I doing it in the wrong order or something? I also tried taking out the glDepthMask calls but that didn''t do anything.
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE); glDepthMask(GL_FALSE); glEnable(GL_STENCIL_TEST); glStencilFunc(GL_ALWAYS, 1, 1); glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE); glDisable(GL_DEPTH_TEST); DrawSurface(); glEnable(GL_DEPTH_TEST); glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE); glDepthMask(GL_TRUE); Am I doing it in the wrong order or something? I also tried taking out the glDepthMask calls but that didn''t do anything.
This is some code I wrote last week when I was playing around w/ the stencil buffer. It makes a window instead of the ground. I know this works... The only other thing would be you need to setup the pixel format for stencil bits and also clear it
----------------------------------------------
//set camera view point
...
glDisable(GL_DEPTH_TEST);
glEnable(GL_STENCIL_TEST);
//set up stencil buffer to replace only w/i window
glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
glStencilFunc(GL_ALWAYS, 1, 1);
//draw our mirror. setts all the pixels in the stencil buffer to 1 which we
//just defined as a mask w/ stencil func()
DrawWindow(windowTexture, winSize);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glEnable(GL_DEPTH_TEST);
//draw to only where stencil buffer is equal to 1
glStencilFunc(GL_EQUAL, 1, 1);
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
//draw the reflection
glPushMatrix();
glScalef(1, 1, -1);
glCullFace(GL_FRONT);
DrawModel();
DrawGround(groundTexture, -24.0);
glCullFace(GL_BACK);
glPopMatrix();
//end drawing reflection
glDisable(GL_STENCIL_TEST);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
//draw blended texture over our window
DrawWindow(windowTexture, winSize);
//draw real ground and model now
DrawModel();
DrawGround(groundTexture, -24.0);
----------------------------------------
g''luck!
----------------------------------------------
//set camera view point
...
glDisable(GL_DEPTH_TEST);
glEnable(GL_STENCIL_TEST);
//set up stencil buffer to replace only w/i window
glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
glStencilFunc(GL_ALWAYS, 1, 1);
//draw our mirror. setts all the pixels in the stencil buffer to 1 which we
//just defined as a mask w/ stencil func()
DrawWindow(windowTexture, winSize);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glEnable(GL_DEPTH_TEST);
//draw to only where stencil buffer is equal to 1
glStencilFunc(GL_EQUAL, 1, 1);
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
//draw the reflection
glPushMatrix();
glScalef(1, 1, -1);
glCullFace(GL_FRONT);
DrawModel();
DrawGround(groundTexture, -24.0);
glCullFace(GL_BACK);
glPopMatrix();
//end drawing reflection
glDisable(GL_STENCIL_TEST);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
//draw blended texture over our window
DrawWindow(windowTexture, winSize);
//draw real ground and model now
DrawModel();
DrawGround(groundTexture, -24.0);
----------------------------------------
g''luck!
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