SER431 Lecture 08

Advanced Graphics
Environment (Planar reflections)
(201809)

Transcript

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   SER 431
   Advanced Graphics
   Lecture 08: Environment (Planar reflections)
   Javier Gonzalez-Sanchez
   javiergs@asu.edu
   PERALTA 230U
   Office Hours: By appointment
   

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   Our Goal
   

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   We are here
   

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   Next step
   

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   Stencil for 3D scenarios
   

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   Step 1. main()
   // main
   void main(int argc, char* argv[]) {
   glutInit(&argc, argv);
   glutInitDisplayMode(
   GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA | GLUT_STENCIL
   );
   // main as usual here...
   }
   

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   Step 2. init()
   // init
   void init() {
   // init as usual here...
   //define the value to use as clean.
   glClearStencil(0);
   }
   

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   Step 3. display()
   void display(void) {
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
   glEnable(GL_STENCIL_TEST);
   glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
   glStencilFunc(GL_ALWAYS, 1, 1);
   glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
   //Render stencil box
   

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   glDisable(GL_DEPTH_TEST);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(-50.0, 50, -50.0, 50.0, 1.0, -1.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
   glPushMatrix();
   glTranslatef(0, 0, 0);
   glBegin(GL_TRIANGLES);
   glVertex2f(-20.0, -20.0);
   glVertex2f( 20.0, -20.0);
   glVertex2f( 0.0, 20.0);
   glEnd();
   glPopMatrix();
   glEnable(GL_DEPTH_TEST);
   

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    // re-enable color and disable stencil
    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
    glStencilFunc(GL_EQUAL, 1, 1);
    glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
    // draw your colors here
    glDisable(GL_STENCIL_TEST);
    glutSwapBuffers();
    }
    

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    New Step 3. display()
    void display(void) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
    //Configure projection and modelview (camera) as usual
    glEnable(GL_STENCIL_TEST);
    glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
    glStencilFunc(GL_ALWAYS, 1, 1);
    glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
    // glDisable(GL_DEPTH_TEST);
    //Render stencil box
    // glDisable(GL_DEPTH_TEST);
    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
    glStencilFunc(GL_NOTEQUAL, 1, 1);
    glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
    // draw your colors here
    glDisable(GL_STENCIL_TEST);
    glutSwapBuffers();
    }
    

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    Next step
    

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    Reflections
    

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    Planar Reflections
    § Easy hack, draw the object twice,
    § One time has glScalef(1,-1,1) to reflect through the floor
    

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    Planar Reflections
    § But, the plain obstruct the boxes below.
    

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    Planar Reflections
    § Make the plain to be blended with the boxes (Disable the light)
    //plane
    glEnable(GL_BLEND);
    glDisable(GL_LIGHTING);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glColor4f(0.7, 0.0, 0.0, 0.3);
    glColor4f(1.0, 1.0, 1.0, 0.3);
    glPushMatrix();
    glTranslatef(-900, 0, -900);
    glCallList(display1);
    glPopMatrix();
    glEnable(GL_LIGHTING);
    glDisable(GL_BLEND);
    

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    Planar Reflections
    § But, the image’s reflection falls off the floor.
    

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    Planar Reflections
    § Stencil can help to maintain the floor
    § Clear stencil to zero.
    § Draw floor polygon with stencil set to one.
    § Then, only draw reflection where stencil is one.
    § Finally, deactivate stencil and draw the rest of the scene.
    

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    Planar Reflections
    glEnable(GL_STENCIL_TEST);
    glDisable(GL_DEPTH_TEST);
    glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
    glStencilFunc(GL_ALWAYS, 1, 0xFFFFFFFF);
    glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
    // Draw the PLAIN for the stencil
    glPushMatrix();
    glTranslatef(-900, 0, -900);
    glCallList(display1);
    glPopMatrix();
    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
    glEnable(GL_DEPTH_TEST);
    glStencilFunc(GL_EQUAL, 1, 0xFFFFFFFF);
    glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
    

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    // boxes reflections
    glPushMatrix();
    glScalef(1.0, -1.0, 1.0);
    glCallList(display2);
    glPopMatrix();
    glPushMatrix();
    glTranslatef(200, 0, 0);
    glScalef(1.0, -1.0, 1.0);
    glCallList(display3);
    glPopMatrix();
    glPushMatrix();
    glTranslatef(-200, 0, 0);
    glScalef(1.0, -1.0, 1.0);
    glCallList(display4);
    glPopMatrix();
    glDisable(GL_STENCIL_TEST);
    

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    Planar Reflections
    

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    One Last Thing
    void display(void) {
    glEnable(GL_CULL_FACE);
    // checks all the faces that are front facing towards
    // the viewer and renders those while discarding all
    // the faces that are back facing
    // Improve performance also!
    glDisable(GL_CULL_FACE);
    }
    

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    Test Yourselves
    § Test 1. Add reflections to your game. For instance, add a mirror or a
    table with a reflective surface
    § Test 2. Add a menu that allows enable/disable reflections
    

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    SER431 Advanced Graphics
    Javier Gonzalez-Sanchez
    javiergs@asu.edu
    Fall 2018
    Disclaimer. These slides can only be used as study material for the class SER431 at ASU. They cannot be
    distributed or used for another purpose.
    

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