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Water Reflection and Opacity

Started by HenriqueRocha Jan 26, 2012 at 4:25 AM 3 replies 4.6k views

Original Post

Jan 26, 2012 at 4:25 AM

Hello again!

I'm having trouble with water opacity and reflection at the same time...

I can do them apart but not at the same time.


 GLvoid DrawGLScene(GLvoid){
 float look[3] = {0.0,0.0,0.0};
 
 double eqr[] = {0.0f,0.0f, -1.0f, 0.0f}; // Plane Equation To Use For The Reflected Objects
 glClearColor(0.0f,0.0f,0.0f,1.0f);
 
 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
 glLoadIdentity();
 add_vector(default_player->dir,look);
 add_vector(default_player->cam,look);
 gluLookAt(default_player->cam[0], default_player->cam[1], default_player->cam[2], look[0], look[1], look[2], 0, 0, 1);
 
 glEnable(GL_STENCIL_TEST); 
 glColorMask(0,0,0,0); 
 glDisable(GL_DEPTH_TEST); 
 glStencilFunc(GL_ALWAYS, 1, 1); 
 glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
 
 RenderWater();
 
 glColorMask(1,1,1,1); 
 glEnable(GL_DEPTH_TEST); 
 glStencilFunc(GL_EQUAL, 1, 1); 
 glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
 /* DRAW */
 
 glEnable(GL_CLIP_PLANE0); 
 glClipPlane(GL_CLIP_PLANE0, eqr); 
 glPushMatrix(); 
 glScalef(1.0f, 1.0f, -1.0f);
 glLightfv(GL_LIGHT1, GL_POSITION,default_player->light_pos);
 gl_all_textures(hash_tex, default_player,map,1); /* terrain */
 glPopMatrix();
 glDisable(GL_CLIP_PLANE0); 
 glDisable(GL_STENCIL_TEST); 
 glLightfv(GL_LIGHT1, GL_POSITION,default_player->light_pos);
 
 RenderSky();
 RenderText();
 
 RenderWater(); /* reflection working but no opactity */
 gl_all_textures(hash_tex, default_player,map,0); /* terrain */
 // RenderWater(); /* opacity working but no reflection */
 
 glutSwapBuffers();
 }

my goal is something like this:

MiguelMartin

Jan 26, 2012 at 12:04 PM

Well, I'm not sure if this will work or not, but assuming that you're using alpha values for the Water (or maybe you need alpha values for the reflection?), you should be enabling blending. Usually you use it like so, you can however use it many different ways though:


 glEnable(GL_BLEND); // Enables blending for OpenGL
 
 
 glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); // Set the Blending function

There's a lot more OpenGL blending functions, but this might do the job, ask Google if you don't like it.

FAQ on Transperancy:
http://www.opengl.or...ransparency.htm

Sorry if you already know this, it just doesn't seem like your enabling blending o:

HenriqueRocha

Jan 26, 2012 at 1:43 PM


 void RenderWater(){
 static float wx=0, wy=0;
 
 glBindTexture(GL_TEXTURE_2D, 5);
 glColor4f(0.3, 0.3, 0.3, 0.6);
 glEnable(GL_BLEND);
 glDisable(GL_LIGHTING);
 if(default_player->lines==0){
 glBegin(GL_QUADS);
 glTexCoord2f(-map->size+wx, -map->size+wy); glVertex3f (-map->size*0.5,-map->size*0.5,0.0);
 glTexCoord2f(+map->size+wx, -map->size+wy); glVertex3f (map->size*0.5,-map->size*0.5,0.0);
 glTexCoord2f(+map->size+wx, +map->size+wy); glVertex3f (map->size*0.5,map->size*0.5,0.0);
 glTexCoord2f(-map->size+wx, +map->size+wy); glVertex3f (-map->size*0.5,map->size*0.5,0.0);
 map->water_level+=0.002;
 if(map->water_level>2*PI)
 map->water_level-=2*PI;
 glEnd();
 wx+=0.002;
 wy+=0.002;
 if(wx>8) wx-=8;
 if(wy>8) wy-=8;
 }
 glDisable(GL_BLEND);
 glDisable(GL_LIGHTING);
 }

I enabled blend in RenderWater().

Hodgman

Jan 26, 2012 at 1:56 PM

The technique that you're using (where you use the stencil buffer to render the regular scene and the "mirrored" scene into the same render-target) is pretty old school.
To achieve robust transparency, I would recommend rendering the "mirrored" scene into a separate render-target, and then compositing the result on top of the regular scene.

gfxgangsta

Jan 26, 2012 at 4:09 PM

I found the following resource particularly useful, but you would have to convert to OpenGL and use shaders:

http://www.riemers.net/eng/Tutorials/XNA/Csharp/Series4/The_water_technique.php

The explanation is pretty good though

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