heightfield.cpp

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#include <GL/gl.h>
#include <assert.h>
#include <string.h>
#include <stdio.h>

#include "heightfield.h"
#include "config.h"
#include "texture.h"


// Height field data
static float *g_hf = NULL;

void initHeightField()
{
  // Validate params
  int W = g_hfW;
  int H = g_hfH;
  assert( W>0 && W*H > 0 );
  // Clear old data
  if (g_hf != NULL) {
    delete[] g_hf;
  }

  // Init new data
  g_hf = new float[W*H];
  memset( g_hf,0, W*H*sizeof(float) );

  // Read data from file
  char filename[500];
  strcpy( filename, g_strResourceDir );
  strcat( filename, g_strHeightFieldFile );
  printf( "Reading height field %s\n", filename );

  FILE *file = fopen( filename, "rb" );
  assert( file != NULL );
  int n;
  if ( (n=fread( g_hf, sizeof(float), W*H, file )) != W*H) {
    printf( "Error loading height field, only %i floats read.", n ); 
  }
  else {
    printf( "read %i floats ... ", n );
  }
}


float gethf( int x, int y ) {
  assert( x>=0 && x<g_hfW );
  assert( y>=0 && y<g_hfH );
  return g_hf[ x + y*g_hfW ];
}



void setDiffuseMaterialColor( const float *mc )
{
  glMaterialfv(GL_FRONT, GL_DIFFUSE, mc );
  glMaterialfv(GL_FRONT, GL_AMBIENT, mc );
  glMaterialfv(GL_FRONT, GL_SPECULAR, colorNone );
  glColor4fv(mc);
}




// render the single quad for the ground
void renderGroundQuad( float w, float h )
{
  static const float transparent_alpha[4] = {1,1,1,0};
  static const float opaque_alpha[4] = {1,1,1,1};


  glBegin( GL_QUADS );

  // At negative w, make transparent if alpha blending is on
  setDiffuseMaterialColor( transparent_alpha );

  // Texture coordinates have to be defined before the vertex
  glTexCoord2f( 0,1 );
  glVertex3f( -w, h, gethf(0,2) );

  glTexCoord2f( 0,0 );
  glVertex3f( -w,-h, gethf(0,0) );


  // At positive w, make opaque if alpha blending is on
  setDiffuseMaterialColor( opaque_alpha );

  glTexCoord2f( 1, 0 );
  glVertex3f( w,-h, gethf(2,0) );

  glTexCoord2f( 1, 1 );
  glVertex3f( w, h, gethf(2,2) );

  glEnd();
}




void drawHeightField( float x, float y, int w, int h )
{
  // Automatic normals do not work correctly for a height field,
  // because there is no interaction between two adjacent strips.
  // In the solution, you will have to compute the normals of
  // the field yourself.
  glEnable( GL_AUTO_NORMAL );

  // Enable the grass texture
  glBindTexture( GL_TEXTURE_2D, texture( TEX_SNOW ));
  glEnable( GL_TEXTURE_2D );

  // Render ground once
  renderGroundQuad( w,h );

  // Allow equal depth buffer values, otherwise the quad is not rendered
  // a second time
  glDepthFunc( GL_LEQUAL );

  // Switch to the second texture
  glDisable( GL_TEXTURE_2D );
  glBindTexture( GL_TEXTURE_2D, texture( TEX_ROCK ));
  glEnable( GL_TEXTURE_2D );

  // Setup blending so that it blends with the framebuffer and the new
  // geometry using the value in the alpha channel as a weight
  glBlendEquation( GL_ADD );
  glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );

  // Switch on alpha blending, and render ground again
  glEnable( GL_BLEND );
  renderGroundQuad( w,h );


  // Reset rendering state
  glDepthFunc( GL_LESS );
  glDisable( GL_BLEND );
  glDisable( GL_TEXTURE_2D );
  glDisable( GL_AUTO_NORMAL );
}

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