Texture Mapping Nehe Demo 6

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Texture MappingNehe Demo 6

• COSC 471
• Matt Devilbiss

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Abstract

• I will explain the coding that pertains to OpenGL
  and the various function calls used to achieve
  texture mapping.

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Outline

• Setting up the functions to texture map
• The contents of those functions
• Declaring a texture object
• Binding the texture
• Specifying the texture
• Drawing the object and applying the texture

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Auxiliary Library

• The header file glaux.h stands for Graphics
  Library Auxiliary
• This demo uses the glaux library
• It emphasizes creating a program by using a small
  amount of code.

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Load the texture

• AUX_RGBImageRec LoadBMP(char Filename)
• Loads the texture bitmap.
• Uses the Glaux library for this purpose

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Loading the texture

• int LoadGLTextures()
• This functions loads the texture and performs the
  binding, and filtering functions.

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Create texture object

• glGenTextures(n, texture0)
• This function returns n unused texture
  identifiers for use.
• glGenTextures(1, texture0)
• We want 1 texture identifier and we are going to
  store it in the array texture

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Bind the texture

• glBindTexture(GL_TEXTURE_2D, texture0)
• This line tells OpenGL we are dealing with a 2D
  texture.
• The last parameter tells it which texture object
  we want to bind

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Specify the texture

• glTexImage2D(GL_TEXTURE_2D, 0, 3,
  TextureImage0-gtsizeX, TextureImage0-gtsizeY,
  0, GL_RGB, GL_UNSIGNED_BYTE, TextureImage0-gtdata
  )
• The first line specifies dimensionality
• The second determines level of detail for mipmaps
• The third tells OpenGL how to store the texture
  in video memory.(RGB)

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Filtering Properties

• glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTE
  R,GL_LINEAR)
• The first parameter refers to the texture target
• The second parameter refers to magnification or
  minification filter.
• The third refers to the method used to determine
  texels at various distance ranges.

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Various setup

• glEnable(GL_TEXTURE_2D)
• Enables 2D texturing
• glShadeModel(GL_SMOOTH)
• Enables smooth shading
• glClearColor(0.0f, 0.0f, 0.0f, 0.5f)
• Sets background to black
• glClearDepth(1.0f)
• Setup depth buffer

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Cont.

• glEnable(GL_DEPTH_TEST)
• Enable depth testing
• glDepthFunc(GL_LEQUAL)
• Specifies how to depth test
• glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST)
• Used to control quality on different machines
• Gets passed GL_FASTEST, GL_NICEST, GL_DONT_CARE.

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Rotating the cube

• glTranslatef(0.0f,0.0f,-5.0f)
• glRotatef(xrot,1.0f,0.0f,0.0f)
• glRotatef(yrot,0.0f,1.0f,0.0f)
• glRotatef(zrot,0.0f,0.0f,1.0f)

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Speed of Rotation

• xrot0.01f
• yrot0.01f
• zrot0.01f
• These control the speed of rotation
• The larger the value the faster the spin.

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Texture Coordinates

• glTexCoord2f(0.0f, 0.0f) glVertex3f(-1.0f,
  -1.0f, 1.0f)

(1.0,1.0)
(0.0, 1.0)
(0.0, 0.0)
(1.0, .0.0)
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Correctly positioning the Texture

• Use the texture coordinates to orient the texture
  as you see fit.
• Simply reverse the coordinates to reverse and
  flip the texture.

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The Main Function

• Draws the scene
• Places the program in a loop
• Waits for user input to end the loop by pressing
  ESC.

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Demonstration

• Now to demonstrate the textured model.