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SER431 Lecture 08

SER431 Lecture 08

Advanced Graphics
Environment (Planar reflections)
(201809)

B546a9b97d993392e4b22b74b99b91fe?s=128

Javier Gonzalez

September 10, 2018
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  1. jgs SER 431 Advanced Graphics Lecture 08: Environment (Planar reflections)

    Javier Gonzalez-Sanchez javiergs@asu.edu PERALTA 230U Office Hours: By appointment
  2. Javier Gonzalez-Sanchez | SER431 | Fall 2018 | 1 jgs

    Our Goal
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    We are here
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    Next step
  5. jgs 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
  13. jgs 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
  24. jgs 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.