4. Simple Shadow Mapping Artefakte eliminieren

Simple Shadow Mapping Artefakte eliminieren

  • ?

    Hallo,

    ich beschäftige mich zur Zeit mit einfachem Shadow Mapping (OpenGL Fixed Function Pipeline).
    Ich habe das Prinzip von Shadow Mapping verstanden.
    Mein Problem ist jetzt die Artefakte 😕, die durch die Ungenauigkeit des z-Buffers entstehen, zu elimieren.
    Ich verstehe nicht genau wie ich glPolygonOffset dazu verwenden soll.

    Deshalb bitte ich euch, dass ihr das einfache Beispiel [shadowmap.c aus dem OpenGL Red Book (Kapitel 14)] so modifiziert,dass die Artefakte verschwinden.
    Kann ja nur an dem fehlenden glPolygonOffset liegen,oder?

    Vielen Dank
    Bastian

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*/
#include "Windows.h"
#include "GLee.h"
#include <stdio.h>
#include <GL/glut.h>
#include <cmath>

#define SHADOW_MAP_WIDTH      512
#define SHADOW_MAP_HEIGHT     512

#define Pi       3.14159265359

GLdouble    fovy      = 60.0;
GLdouble    nearPlane = 10.0;
GLdouble    farPlane  = 100.0;

GLfloat     angle = 0.0;
GLfloat     torusAngle = 0.0;

GLfloat     lightPos[] = { 25.0, 25.0, 25.0, 1.0 };
GLfloat     lookat[] = { 0.0, 0.0, 0.0 };
GLfloat     up[] = { 0.0, 0.0, 1.0 };

GLboolean showShadow = GL_FALSE;

void
init( void )
{
    GLfloat  white[] = { 1.0, 1.0, 1.0, 1.0 };

    glTexImage2D( GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT,
  		  SHADOW_MAP_WIDTH, SHADOW_MAP_HEIGHT, 0,
		  GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, NULL );

    glLightfv( GL_LIGHT0, GL_POSITION, lightPos );
    glLightfv( GL_LIGHT0, GL_SPECULAR, white );
    glLightfv( GL_LIGHT0, GL_DIFFUSE, white );

    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LEQUAL );
    glTexParameteri( GL_TEXTURE_2D, GL_DEPTH_TEXTURE_MODE, GL_LUMINANCE );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE,
		     GL_COMPARE_R_TO_TEXTURE );

    glTexGeni( GL_S, GL_TEXTURE_GEN_MODE, GL_OBJECT_LINEAR );
    glTexGeni( GL_T, GL_TEXTURE_GEN_MODE, GL_OBJECT_LINEAR );
    glTexGeni( GL_R, GL_TEXTURE_GEN_MODE, GL_OBJECT_LINEAR );
    glTexGeni( GL_Q, GL_TEXTURE_GEN_MODE, GL_OBJECT_LINEAR );

    glColorMaterial( GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE );

    glCullFace( GL_BACK );

    glEnable( GL_DEPTH_TEST );
    glEnable( GL_LIGHT0 );
    glEnable( GL_LIGHTING );
    glEnable( GL_TEXTURE_2D );
    glEnable( GL_TEXTURE_GEN_S );
    glEnable( GL_TEXTURE_GEN_T );
    glEnable( GL_TEXTURE_GEN_R );
    glEnable( GL_TEXTURE_GEN_Q );
    glEnable( GL_COLOR_MATERIAL );
    glEnable( GL_CULL_FACE );
}

void
reshape( int width, int height )
{
    glViewport( 0, 0, width, height );

    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    gluPerspective( fovy, (GLdouble) width/height, nearPlane, farPlane );
    glMatrixMode( GL_MODELVIEW );
}

void
idle( void )
{
    angle += Pi / 10000;
    torusAngle += .1;
    glutPostRedisplay();
}

void
keyboard( unsigned char key, int x, int y )
{
    switch( key ) {
    case 27:  /* Escape */
      exit( 0 );
      break;

    case 't': {
        static GLboolean textureOn = GL_TRUE;
        textureOn = !textureOn;
        if ( textureOn )
	glEnable( GL_TEXTURE_2D );
        else
	glDisable( GL_TEXTURE_2D );
      }
      break;

    case 'm': {
        static GLboolean compareMode = GL_TRUE;
        compareMode = !compareMode;
        printf( "Compare mode %s\n", compareMode ? "On" : "Off" );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE,
		         compareMode ? GL_COMPARE_R_TO_TEXTURE : GL_NONE );
      }
      break;

    case 'f': {
        static GLboolean funcMode = GL_TRUE;
        funcMode = !funcMode;
        printf( "Operator %s\n", funcMode ? "GL_LEQUAL" : "GL_GEQUAL" );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC,
		         funcMode ? GL_LEQUAL : GL_GEQUAL );
      }
      break;

    case 's':
      showShadow = !showShadow;
      break;

    case 'p': {
        static GLboolean  Animate = GL_TRUE;
        Animate = !Animate;
        glutIdleFunc( Animate ? idle : 0 );
      }
      break;
    }

    glutPostRedisplay();
}

void
transposeMatrix( GLfloat m[16] )
{
    GLfloat  tmp;
#define Swap( a, b )    tmp = a; a = b; b = tmp
    Swap( m[1],  m[4]  );
    Swap( m[2],  m[8]  );
    Swap( m[3],  m[12] );
    Swap( m[6],  m[9]  );
    Swap( m[7],  m[13] );
    Swap( m[11], m[14] );
#undef Swap
}

void
drawObjects( GLboolean shadowRender )
{
    GLboolean textureOn = glIsEnabled( GL_TEXTURE_2D );

    if ( shadowRender )
        glDisable( GL_TEXTURE_2D );

    if ( !shadowRender ) {
        glNormal3f( 0, 0, 1 );
        glColor3f( 1, 1, 1 );
        glRectf( -20.0, -20.0, 20.0, 20.0 );
    }

    glPushMatrix();
    glTranslatef( 11, 11, 11 );
    glRotatef( 54.73, -5, 5, 0 );
    glRotatef( torusAngle, 1, 0, 0 );
    glColor3f( 1, 0, 0 );
    glutSolidTorus( 1, 4, 8, 36 );
    glPopMatrix();

    glPushMatrix();
    glTranslatef( -8, 9, 2 );
    glColor3f( 0, 0, 1 );
    glutSolidCube( 4 );
    glPopMatrix();

    glPushMatrix();
    glTranslatef( lightPos[0], lightPos[1], lightPos[2] );
    glColor3f( 1, 1, 1 );
    glutWireSphere( 0.5, 6, 6 );
    glPopMatrix();

    if ( shadowRender && textureOn )
        glEnable( GL_TEXTURE_2D );
}

void
generateShadowMap( void )
{
    GLint    viewport[4];
    GLfloat  lightPos[4];

    glGetLightfv( GL_LIGHT0, GL_POSITION, lightPos );
    glGetIntegerv( GL_VIEWPORT, viewport );

    glViewport( 0, 0, SHADOW_MAP_WIDTH, SHADOW_MAP_HEIGHT );

    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    glMatrixMode( GL_PROJECTION );
    glPushMatrix();
    glLoadIdentity();
    gluPerspective( 80.0, 1.0, 10.0, 1000.0 );
    glMatrixMode( GL_MODELVIEW );

    glPushMatrix();
    glLoadIdentity();
    gluLookAt( lightPos[0], lightPos[1], lightPos[2],
	       lookat[0], lookat[1], lookat[2],
	       up[0], up[1], up[2] );

    drawObjects( GL_TRUE );

    glPopMatrix();
    glMatrixMode( GL_PROJECTION );
    glPopMatrix();
    glMatrixMode( GL_MODELVIEW );

    glCopyTexImage2D( GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, 0, 0,
		      SHADOW_MAP_WIDTH, SHADOW_MAP_HEIGHT, 0 );

    glViewport( viewport[0], viewport[1], viewport[2], viewport[3] );

    if ( showShadow ) {
      GLfloat depthImage[SHADOW_MAP_WIDTH][SHADOW_MAP_HEIGHT];
      glReadPixels( 0, 0, SHADOW_MAP_WIDTH, SHADOW_MAP_HEIGHT,
		    GL_DEPTH_COMPONENT, GL_FLOAT, depthImage );
      glWindowPos2f( viewport[2]/2, 0 );
      glDrawPixels( SHADOW_MAP_WIDTH, SHADOW_MAP_HEIGHT, GL_LUMINANCE,
		    GL_FLOAT, depthImage );
      glutSwapBuffers();
    }
}

void
generateTextureMatrix( void )
{
    GLfloat  tmpMatrix[16];

    /*
     *  Set up projective texture matrix.  We use the GL_MODELVIEW matrix
     *    stack And OpenGL matrix commands To make the matrix.
     */
    glPushMatrix();
    glLoadIdentity();
    glTranslatef( 0.5, 0.5, 0.0 );
    glScalef( 0.5, 0.5, 1.0 );
    gluPerspective( 60.0, 1.0, 1.0, 1000.0 );
    gluLookAt( lightPos[0], lightPos[1], lightPos[2],
	       lookat[0], lookat[1], lookat[2],
	       up[0], up[1], up[2] );
    glGetFloatv( GL_MODELVIEW_MATRIX, tmpMatrix );
    glPopMatrix();

    transposeMatrix( tmpMatrix );

    glTexGenfv( GL_S, GL_OBJECT_PLANE, &tmpMatrix[0] );
    glTexGenfv( GL_T, GL_OBJECT_PLANE, &tmpMatrix[4] );
    glTexGenfv( GL_R, GL_OBJECT_PLANE, &tmpMatrix[8] );
    glTexGenfv( GL_Q, GL_OBJECT_PLANE, &tmpMatrix[12] );
}

void
display( void )
{
    GLfloat  radius = 30;

glEnable(GL_POLYGON_OFFSET_FILL);
glPolygonOffset(-1,-1);

    generateShadowMap();
    generateTextureMatrix();

glDisable(GL_POLYGON_OFFSET_FILL);

    if ( showShadow )
      return;

    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    glPushMatrix();
    gluLookAt( radius*cos(angle), radius*sin(angle), 30,
	       lookat[0], lookat[1], lookat[2],
	       up[0], up[1], up[2] );
    drawObjects( GL_FALSE );
    glPopMatrix();

    glutSwapBuffers();
}

int
main( int argc, char** argv )
{
    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE );
    glutInitWindowSize( 512, 512 );
    glutInitWindowPosition( 100, 100 );
    glutCreateWindow( argv[0] );

    init();

    glutDisplayFunc( display );
    glutReshapeFunc( reshape );
    glutKeyboardFunc( keyboard );
    glutIdleFunc( idle );

    glutMainLoop();

    return 0;
}
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  • ?

    Ich denke mal, ohne Shader wird das nicht so leicht gehen.
    Wenn du das ShadowMapping via GLSL durchführst, kannst du PCF oder GaussianBlur Filter anwenden, wodurch die Übergänge weich werden und das Problem gelöst ist.
    Ohne Shader kenn ich da (leider) keine Lösung! Falls es eine gibt, wäre ich auch daran interessiert.

    0
  • ?

    Werde demnächst GLSL lernen.
    Ich wäre denoch sehr an einer Fixed Function Pipeline Lösung interessiert.
    Echt Schade,dass dieses Beispiel aus dem Red Book nicht auf die Hauptptroblematik bei Shadow Mapping eingeht 😞

    0
  • ?

    Hier hab ich Screenshots:
    https://picasaweb.google.com/107094611410670291743/March172012?authkey=Gv1sRgCNXg3p3FnpvHeg

    0
  • ?

    Schau dir mal die pdf an:
    http://www.uni-koblenz.de/~cg/Studienarbeiten/ShadowMappingNicoHempe.pdf

    Trapeziondal Shadow Maps verbessern die Sache schon ganz gut.

    0
  • ?

    Danke soweit.
    Aber kann mir jemand erklären, warum ich dieses Problem eben NICHT so ohne weiteres mit glDepthOffset lösen kann? Es liegt doch ausschließlich an der z-Buffer Ungenauigkeit,welche ich doch mit einem Offset "ausgleichen" könnte,oder?

    0
  • ?

    Weil du letztendlich trotzdem nur eine begrenzte Genauigkeit in der Tiefenmap hast und dies (leider) noch nicht weiche Kanten erzeugt. Damit lässt sich z.B. das SelfShadowing von Objekten beheben aber sowas ist damit nicht drin.

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