9.4 Highlights

The procedure you follow to produce highlights is explained in the Programming Manual in Chapter 11.7.4, "Specular Highlights," so here we will give just a simple explanation using the source from the gfx9.c sample program.

Whereas the Programming Manual presents sample code to position two highlight light-sources, the gfx9.c sample program makes use of only one highlight. Thus, you will probably want to look at gfx9.c to see how to position just one highlight light-source.


9.4.1 Preparing the Structure

To perform lighting using highlights, you define the LookAt type variable and Hilite type variable, and pass these to the guLookAtHilite function and initialize. The guLookAtHilite function takes a number of arguments, but none are very difficult to understand. For details, please see the Function Reference.

List 9-1 
  guLookAtHiliteF(fmat2, &lookat, &hilite,
                0.0, 0.0, 50.0,
                0.0, 0.0, 0.0,
                0.0, 1.0, 0.0,
                0.0, 1.0, 0.0,   /* Direction of highlight light-source  */
                0.0, 0.0, 1.0,   /* A non-zero value even when not used  */
                __TEXTURE_WIDTH__,
                __TEXTURE_HEIGHT__);

9.4.2 Preparing the Light

Although the direction of the highlight light-source is specified in guLookAtHilite, you also need to define a light structure that points in the same direction. In the case of the gfx9.c sample program, diffuse light is also used at the same time as a highlight.

List 9-2 
Lights1 light = gdSPDefLights1( 0,   0, 50,  /* Blue ambient light  */
                              250, 150, 30,  /* Gold diffuse light */
                                0, 127,  0); /* Direction toward diffuse light */

9.4.3 Loading the Texture

g The texture coordinate scaling parameters and the primitive tile are specified in gSPTexture. G_TX_RENDERTILE, which is a macro constant defined in <gbi.h>, connotes Tile0. If you use either gDPLoadTextureBlock or gDPLoadTextureTile, then the texture will be automatically loaded to the G_TX_RENDERTILE tile. The color that is used for highlight color is the one set for primitive color.

List 9-3 
  * Enable textures, set scaling parameters */
  gSPTexture(glistp++,
            (__TEXTURE_WIDTH__  - 1) << 6,
            (__TEXTURE_HEIGHT__ - 1) << 6,
            0, G_TX_RENDERTILE, G_ON);
  /* (Parts have been omitted) */
  /*
   *  Load highlight texture (image i8hilite)
@ *  Wrapping is turned on
   */
  gDPLoadTextureBlock(glistp++,
                i8hilite,             /* Pointer to texture image */
                G_IM_FMT_I,           /* Texel format  */
                G_IM_SIZ_8b,          /* Texel size  */
                __TEXTURE_WIDTH__,    /* Image width  */
                __TEXTURE_HEIGHT__,   /* Image height  */
                0,            /* LUT (highlight) index. (Not used here)*/
                G_TX_WRAP | G_TX_NOMIRROR,
                              /* Clamp, wrap, mirror flags in s direction  */
                G_TX_WRAP | G_TX_NOMIRROR,
                              /* Clamp, wrap, mirror flags in t direction */
                __TEXTURE_BITS_X__,        /* s mask  */
                __TEXTURE_BITS_Y__,        /* t mask  */
                G_TX_NOLOD, G_TX_NOLOD);   /* Shift (No shift here) */
  /* The primitive color becomes the color of the highlight light  */
  gDPSetPrimColor(glistp++, 0, 0, 255, 255, 255, 255);

9.4.4 Other Commands

To use highlight textures, you also need to set the various modes with the following commands. Note that G_TEXTURE_GEN has been added to geometry mode.

List 9-4 
  gSPLookAt(glistp++, &lookat);
  /* Please set G_TEXTURE_GEN in geometry mode  */
  gSPSetGeometryMode(glistp++, G_TEXTURE_GEN | G_LIGHTING |
                     G_ZBUFFER | G_SHADE | G_SHADING_SMOOTH | G_CULL_BACK);
  /* G_CC_HILITERGB = PRIMITIVE, SHADE, TEXEL0, SHADE, 0, 0, 0, SHADE */
  gDPSetCombineMode(glistp++, G_CC_HILITERGB, G_CC_HILITERGB);
  /* Light position  */
  gSPSetLights1(glistp++, light);
  /* Set highlight texture tile */
  gDPSetHilite1Tile(glistp++, G_TX_RENDERTILE, &hilite,
                              __TEXTURE_WIDTH__, __TEXTURE_HEIGHT__);

Figure 9-2 Screen shots of gfx9.c sample program with __HILITE__ defined.