This document discusses techniques for creating skyboxes and terrain in OpenGL graphics. It explains how to create a skydome using skybox textures and then generate terrain by mapping height data from a heightmap texture onto a grid and rendering it with additional textures. Methods are provided for scaling, translating and drawing the terrain as well as querying the heightmap to position the camera above the terrain. Advanced techniques discussed include using quad trees for efficient searching, multitexturing, adding detail textures, and raycasting against the terrain.

1. Mohammad Shaker
mohammadshaker.com
@ZGTRShaker
2015
OpenGL Graphics
L07-SKYBOX&TERRAIN

2. How to create the Sky?

3. Skydome and Skybox

4. Skydome

5. SkyBox

6. SkyBox
Just 6 textures!
See the code

7. SkyBox

8. SkyBox

9. SkyBox

10. SkyBox

11. Now, How to create the ground?!

12. Terrain

13. Terrain
Grid

14. Terrain
Grid Height Map
+

15. Terrain
Grid
=
Height Map
+

16. Terrain
+
Colored Terrain

17. Terrain
Texture 24 bits
+
Colored Terrain
+

18. Terrain
=
Texture 24 bits
+
3D TerrainColored Terrain
+

19. Planetside’s
Terragen

20. Planetside’s Terragen

21. Terrain’s Height Map Representation

22. Terrain’s Height Map Representation

23. Terrain, The Code

24. Terrain
• #include “texture.h”
• #include “heightMap.h”
• Define
int terraintexture ; // index to terrain texture
GLubyte * HeightData ; // vector (saving heights)
int TerrainSize = 512; // width = height = 512
float step = 1/512.0; // step for texture
• InitGL()
terraintexture = LoadTexture("imagesterrain texture.bmp");
HeightData = new GLubyte(TerrainSize*TerrainSize);
HeightData = LoadHeightMap("imagesterrain height.bmp");

25. Terrain – Draw Algorithm
initTerrainPositionX = TerrainSize/2.0f; initTerrainPositionZ = TerrainSize/2.0f; initTerrainPositionY = 0;
glPushMatrix();
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D,terraintexture);
glScalef(scaleX,scaleY,scaleZ);
glTranslatef(-initTerrainPositionX, initTerrainPositionY, -initTerrainPositionZ);
for (int i = 3 ; i<TerrainSize-3 ; i++)
{
glBegin(GL_TRIANGLE_STRIP);
for (int j = 3 ; j < TerrainSize -3; j++)
{
glTexCoord2f(j*step,i*step);
glVertex3f(i, GetValue(i,j), j);
glTexCoord2f((j+1)*step,i*step);
glVertex3f(i, GetValue(i,j+1), j+1);
glTexCoord2f(j*step,(i+1)*step);
glVertex3f(i+1, GetValue(i+1,j), j);
glTexCoord2f((j+1)*step,(i+1)*step);
glVertex3f(i+1, GetValue(i+1,j+1), j+1);
}
glEnd();
}
glDisable(GL_TEXTURE_2D);
glPopMatrix();

26. Terrain – Draw Algorithm
initTerrainPositionX = TerrainSize/2.0f; initTerrainPositionZ = TerrainSize/2.0f; initTerrainPositionY = 0;
glPushMatrix();
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D,terraintexture);
glScalef(scaleX,scaleY,scaleZ);
glTranslatef(-initTerrainPositionX, initTerrainPositionY, -initTerrainPositionZ);
for (int i = 3 ; i<TerrainSize-3 ; i++)
{
glBegin(GL_TRIANGLE_STRIP);
for (int j = 3 ; j < TerrainSize -3; j++)
{
glTexCoord2f(j*step,i*step);
glVertex3f(i, GetValue(i,j), j);
glTexCoord2f((j+1)*step,i*step);
glVertex3f(i, GetValue(i,j+1), j+1);
glTexCoord2f(j*step,(i+1)*step);
glVertex3f(i+1, GetValue(i+1,j), j);
glTexCoord2f((j+1)*step,(i+1)*step);
glVertex3f(i+1, GetValue(i+1,j+1), j+1);
}
glEnd();
}
glDisable(GL_TEXTURE_2D);
glPopMatrix();
Scale the terrain

27. Terrain – Draw Algorithm
initTerrainPositionX = TerrainSize/2.0f; initTerrainPositionZ = TerrainSize/2.0f; initTerrainPositionY = 0;
glPushMatrix();
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D,terraintexture);
glScalef(scaleX,scaleY,scaleZ);
glTranslatef(-initTerrainPositionX, initTerrainPositionY, -initTerrainPositionZ);
for (int i = 3 ; i<TerrainSize-3 ; i++)
{
glBegin(GL_TRIANGLE_STRIP);
for (int j = 3 ; j < TerrainSize -3; j++)
{
glTexCoord2f(j*step,i*step);
glVertex3f(i, GetValue(i,j), j);
glTexCoord2f((j+1)*step,i*step);
glVertex3f(i, GetValue(i,j+1), j+1);
glTexCoord2f(j*step,(i+1)*step);
glVertex3f(i+1, GetValue(i+1,j), j);
glTexCoord2f((j+1)*step,(i+1)*step);
glVertex3f(i+1, GetValue(i+1,j+1), j+1);
}
glEnd();
}
glDisable(GL_TEXTURE_2D);
glPopMatrix();
Translate the terrain

28. Terrain – Draw Algorithm
initTerrainPositionX = TerrainSize/2.0f; initTerrainPositionZ = TerrainSize/2.0f; initTerrainPositionY = 0;
glPushMatrix();
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D,terraintexture);
glScalef(scaleX,scaleY,scaleZ);
glTranslatef(-initTerrainPositionX, initTerrainPositionY, -initTerrainPositionZ);
for (int i = 3 ; i<TerrainSize-3 ; i++)
{
glBegin(GL_TRIANGLE_STRIP);
for (int j = 3 ; j < TerrainSize -3; j++)
{
glTexCoord2f(j*step,i*step);
glVertex3f(i, GetValue(i,j), j);
glTexCoord2f((j+1)*step,i*step);
glVertex3f(i, GetValue(i,j+1), j+1);
glTexCoord2f(j*step,(i+1)*step);
glVertex3f(i+1, GetValue(i+1,j), j);
glTexCoord2f((j+1)*step,(i+1)*step);
glVertex3f(i+1, GetValue(i+1,j+1), j+1);
}
glEnd();
}
glDisable(GL_TEXTURE_2D);
glPopMatrix();
Drawing the terrain primitives

29. Querying Height

30. Terrain – Querying Height
MyCamera.Position.y = (float)(GetValue(
(int)((MyCamera.Position.x + initTerrainPositionX) * scaleX),
(int)((MyCamera.Position.z + initTerrainPositionZ) * scaleZ)
))
*scaleY
+15;

31. Terrain – Querying Height
MyCamera.Position.y = (float)(GetValue(
(int)((MyCamera.Position.x + initTerrainPositionX) * scaleX),
(int)((MyCamera.Position.z + initTerrainPositionZ) * scaleZ)
))
*scaleY
+15;
Getting the correspondent map height
at the camera’s current position

32. Terrain – Querying Height
MyCamera.Position.y = (float)(GetValue(
(int)((MyCamera.Position.x + initTerrainPositionX) * scaleX),
(int)((MyCamera.Position.z + initTerrainPositionZ) * scaleZ)
))
*scaleY
+15;
Compensate for any translation on X
and/or Z axis

33. Terrain – Querying Height
MyCamera.Position.y = (float)(GetValue(
(int)((MyCamera.Position.x + initTerrainPositionX) * scaleX),
(int)((MyCamera.Position.z + initTerrainPositionZ) * scaleZ)
))
*scaleY
+15;
Scale it by how much you scaled the
terrain on X and Z axis

34. Terrain – Querying Height
MyCamera.Position.y = (float)(GetValue(
(int)((MyCamera.Position.x + initTerrainPositionX) * scaleX),
(int)((MyCamera.Position.z + initTerrainPositionZ) * scaleZ)
))
*scaleY
+15;
And scale the y value in the height map
by how much the terrain is Y scaled

35. Terrain – Querying Height
MyCamera.Position.y = (float)(GetValue(
(int)((MyCamera.Position.x + initTerrainPositionX) * scaleX),
(int)((MyCamera.Position.z + initTerrainPositionZ) * scaleZ)
))
*scaleY
+15; And hover above the position a bit

36. Advanced Techniques

37. Quad Tree for Fast Searching in Big Worlds

38. Multitexturing
• Just another custom shader!

39. Detailing

40. Multitexturing

41. Ray and Terrain Collision – Binary Tree Search

42. Using Custom Shaders