SER431 Lecture 07

Advanced Graphics
Environment (Fog)
(201809)

Transcript

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   SER 431
   Advanced Graphics
   Lecture 07: Environment
   Javier Gonzalez-Sanchez
   javiergs@asu.edu
   PERALTA 230U
   Office Hours: By appointment
   

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   Fog
   

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   Fog
   

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   Add this Code to your init() method
   glEnable(GL_FOG);
   // specifies the equation to be used to compute the fog blend factor.
   // GL_LINEAR, GL_EXP, and GL_EXP2.
   // initial fog mode is GL_EXP
   glFogi(GL_FOG_MODE, GL_LINEAR);
   // the fog color. Color components are in the range [0,1].
   // the initial fog color is (0, 0, 0, 0).
   GLfloat fogColor[4] = { 0.5, 0.5, 0.5, 1.0 };
   glFogfv(GL_FOG_COLOR, fogColor);
   //Used in exponential fog equations. The initial fog density is 1.
   // Only nonnegative densities are accepted.
   glFogf(GL_FOG_DENSITY, 0.25);
   // the near distance used in the linear fog equation. The initial near distance is 0
   glFogf(GL_FOG_START, 10.0);
   // the far distance used in the linear fog equation. The initial far distance is 1.
   glFogf(GL_FOG_END, 6000.0);
   

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   Fog Mode and Density
   

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   Test Yourselves
   § Test 1. Add fog to your quiz 2
   § Test 2. Add a menu that allows enable/disable the fog
   

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   Reflection and Shadows
   

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   Reflection and Shadows
   We will use the Stencil Buffer
   

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   Buffers (Color + Depth)
   § An extra data buffer, in addition to the color buffer and depth buffer
   § Depth-buffer. it keep track of the depth of every pixel on the screen
   

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    Buffers (Stencil)
    § Stencil-buffer. it is used to limit the area of rendering (stenciling)
    § Usually contains 8 bits per stencil value that amounts to a total
    of 256 different stencil values
    

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    Example
    

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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);
    //Start using the stencil
    glEnable(GL_STENCIL_TEST);
    //Disable writing colors in frame buffer
    glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
    glStencilFunc(GL_ALWAYS, 1, 1); //Place a 1 where rendered
    //Replace where rendered
    glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
    //Render stencil box
    glDisable(GL_DEPTH_TEST);
    

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    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();
    

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    // re-enable color
    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
    // where a 1 was not rendered.. try GL_NOTEQUAL
    glStencilFunc(GL_EQUAL, 1, 1);
    // keep the pixel
    glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
    glEnable(GL_DEPTH_TEST);
    // display as usual here...
    glDisable(GL_STENCIL_TEST);
    glutSwapBuffers();
    }
    

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    Example
    

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    Next step
    

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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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