GL_WIN_phong_shading

Name

    WIN_phong_shading

Name Strings

    GL_WIN_phong_shading

Version

    $Date: 1997/4/3 

Number

    113

Dependencies

    None

Overview

    WIN_phong_shading enables rendering Phong shaded primitives using OpenGL.
    Phong shading is a well known shading technique documented 
    in most graphics texts. 
    
    As opposed to Gouraud (or smooth) shading, which simply calculates the 
    normals at the vertices and then interpolates the colors of the pixels, 
    Phong shading involves interpolating an individual normal for every pixel,
    and then applying the shading model to each pixel based on its normal 
    component. 

    While Phong shading requires substantially more computation than does 
    Gouraud shading, the resulting images are more realistic, especially if the
    primitives are large. 

Issues

    None

New Procedures and Functions

    None

New Tokens

    Accepted by the <mode> parameter of ShadeModel:

    PHONG_WIN                  0x80EA

    May be returned by GetBooleanv, GetDoublev, GetIntegerv, and GetFloatv
    when their <pname> parameter is SHADE_MODEL:

    PHONG_WIN                  0x80EA

    Accepted by the <target> parameter of Hint, and <pname> parameter of
    GetBooleanv, GetDoublev, GetFloatv and GetIntegerv:

    PHONG_HINT_WIN             0x80EB

Additions to Chapter 2 of the 1.1 Specification (OpenGL Operation)
    First sentence in Section 2.13, "Colors and Coloring", 'Figure 2.8 
    diagrams..' should be modified as below:

    "Figure 2.8 diagrams the processing of colors before rasterization when 
    the primitives are not phong-shaded."

    After the last paragraph of Section 2.13, "Colors and Coloring", the

    following paragraph is added:

    "The WIN_phong_shading extension is used to indicate that the primitives
    should be phong shaded. In which case, the lighting, if enabled, is 
    applied at the time of rasterization to each pixel to obtain a color for
    that pixel. The lighting computation used is consistant with the GL 
    lighting model described in Section 2.13.1. If the primitive is clipped,
    then normals (and eye coordinates) must be computed for the vertices
    introduced or modified by clipping."
    
    Rename Section 2.13.7 to "Shading Models" and. Keep the first paragraph as
    it is. Add the following new paragraph after the one ending in 
    "...Table 2.9 summarizes the possibilities":

    "A primitive may be phong-shaded, meaning that instead of the the color
    being interpolated, the normal (and the eye coordinate) are interpolated 
    across the primitive, and the lighting (if enabled) is applied per pixel
    at the time of rasterization. If the other material properties change 
    within a primitive, either by ColorMaterial or explicitly changing the 
    material property using the Material command, they must be also be 
    interpolated along with the normal (and eye coordinate). However, for 
    efficiency's sake, an implementation may choose to ignore the effects of
    the changes in material properties across a primitive. 
    If the lighting is disabled, or if the primitive is a point, it is 
    equivalent to regular smooth shading.

    Implementations may also choose to approximate phong-shading by smart
    interpolation techniques (some of which are described in graphics 
    literature). Using such algorithms, they may choose to tradeoff visual 
    fidelity for speed of rendering. For such a case a phong hint state,
    discussed in section 5.6, can be used."

    Modify the paragraph beginning with "Flatshading is controlled by....." 
    to the following:

    "Phong-shading and flatshading are controlled by 
        
        void ShadeModel( enum mode);

    mode value must be one of the symbolic constant SMOOTH, FLAT or 
    PHONG_WIN. If mode is SMOOTH (the initial state), vertex colors are 
    treated individually. If mode is FLAT, flatshading is turned on. If mode
    is PHONG_WIN phong-shading is turned on. ShadeModel thus requires 2 bits
    of state."

    Rename Section 2.13.8 to "Color, Texture, Normal and Eye-Coordinate 
    Clipping". Add the following line after "The method is exactly...":

    "If phong-shading is turned on, the normals and eye coordinates must be
    computed for the newly generated vertices. The normals and the 
    eye-coordinates for these vertices are computed in exactly the manner
    described for color clipping. In addition, unless the implementation
    chooses to ignore changes in material properties within the primitive, 
    they should be computed for the new vertices analogously."

Additions to Chapter 3 of the 1.1 Specification (Rasterization)

    After the sentence "The second ...." in the first paragraph, add the
    sentence:

    "If phong-shading is enabled, the color for the square is also computed 
    in this stage."

    Modify the first line of the second paragraph to:
    "A grid square along with its parameters of assigned color, z (depth),
    texture coordinates, normal and eye coordinates (for phong shading)"

    In Section 3.4.1 "Basic Line Segment Rasterization", modify the line

    "The value of an associated datum f......." after equation 3.1 to:

    "The value of an associated datum f for the fragment, whether it be R, G,
    B, or A (in RGBA mode) or a color index (in color index mode), or normal,
    eye coordinate or material properties (when phong-shaded), or the s, t, or
    r texture coordinate .......... is found as"

Additions to Chapter 4 of the 1.1 Specification (Per-Fragment Operations and the Frame Buffer)

    None

Additions to Chapter 5 of the 1.1 Specification (Special Functions)

    In Section 5.6, "Hints", add the following phrase to the line beginning
    "target may be one of .......":

    "and PHONG_HINT_WIN, indicating the desired quality of phong shading."

Additions to Chapter 6 of the 1.0 Specification (State and State Requests)

    None

Dependencies on other extensions

    None

Errors

    None

New State
                                                Initial
    Get Value				Get Command	Type	Value 	    Attrib
    ---------				-----------	----	-------	    ------
    PHONG_HINT_WIN          		GetIntegerv 	Z3      DONT_CARE   hint

New Implementation Dependent State

    None

Implementation Support

   List of OpenGL implementations supporting the GL_WIN_phong_shading extension

Original File

   Original text file for the GL_WIN_phong_shading extension