195 lines
8.2 KiB
HTML
195 lines
8.2 KiB
HTML
<HTML>
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<HEAD>
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<META name=vsisbn content="1576101746">
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<META name=vstitle content="Michael Abrash's Graphics Programming Black Book, Special Edition">
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<META name=vsauthor content="Michael Abrash">
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<META name=vspublisher content="The Coriolis Group">
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<META name=vspubdate content="07/01/97">
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<META name=vscategory content="Web and Software Development: Game Development,Web and Software Development: Graphics and Multimedia Development">
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<TITLE>Michael Abrash's Graphics Programming Black Book Special Edition: 3-D Shading</TITLE>
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<!-- HEADER -->
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<!-- Empty Reference Subhead -->
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<!--ISBN=1576101746//-->
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<!--TITLE=Michael Abrash's Graphics Programming Black Book Special Edition//-->
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<!--AUTHOR=Michael Abrash//-->
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<!--PUBLISHER=The Coriolis Group, Inc.//-->
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<!--CHAPTER=54//-->
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<!--PAGES=1025-1027//-->
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<!--UNASSIGNED1//-->
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<!--UNASSIGNED2//--></HEAD><BODY LINK=#0000FF ALINK=#000099 VLINK=#0000FF BGCOLOR=#FFFFFF>
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<CENTER>
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<TABLE BORDER>
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<TR>
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<TD><A HREF="54-03.html">Previous</A></TD>
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<TD><A HREF="index.html">Table of Contents</A></TD>
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<TD><A HREF="54-05.html">Next</A></TD>
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</TR>
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</TABLE>
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</CENTER>
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<P><BR></P>
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<P><B>LISTING 54.2 DRAWPOBJ.C</B></P>
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<!-- CODE //-->
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<PRE>
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/* Draws all visible faces in the specified polygon-based object. The object
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must have previously been transformed and projected, so that all vertex
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arrays are filled in. Ambient and diffuse shading are supported. */
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#include "polygon.h"
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void DrawPObject(PObject * ObjectToXform)
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{
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int i, j, NumFaces = ObjectToXform->NumFaces, NumVertices;
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int * VertNumsPtr, Spot;
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Face * FacePtr = ObjectToXform->FaceList;
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Point * ScreenPoints = ObjectToXform->ScreenVertexList;
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PointListHeader Polygon;
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Fixedpoint Diffusion;
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ModelColor ColorTemp;
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ModelIntensity IntensityTemp;
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Point3 UnitNormal, *NormalStartpoint, *NormalEndpoint;
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long v1, v2, w1, w2;
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Point Vertices[MAX-POLY-LENGTH];
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/* Draw each visible face (polygon) of the object in turn */
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for (i=0; i<NumFaces; i++, FacePtr++) {
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/* Remember where we can find the start and end of the polygon's
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unit normal in view space, and skip over the unit normal endpoint
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entry. The end and start points of the unit normal to the polygon
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must be the first and second entries in the polgyon's vertex list.
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Note that the second point is also an active polygon vertex */
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VertNumsPtr = FacePtr->VertNums;
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NormalEndpoint = &ObjectToXform->XformedVertexList[*VertNumsPtr++];
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NormalStartpoint = &ObjectToXform->XformedVertexList[*VertNumsPtr];
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/* Copy over the face's vertices from the vertex list */
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NumVertices = FacePtr->NumVerts;
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for (j=0; j<NumVertices; j++)
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Vertices[j] = ScreenPoints[*VertNumsPtr++];
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/* Draw only if outside face showing (if the normal to the polygon
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in screen coordinates points toward the viewer; that is, has a
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positive Z component) */
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v1 = Vertices[1].X - Vertices[0].X;
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w1 = Vertices[NumVertices-1].X - Vertices[0].X;
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v2 = Vertices[1].Y - Vertices[0].Y;
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w2 = Vertices[NumVertices-1].Y - Vertices[0].Y;
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if ((v1*w2 - v2*w1) > 0) {
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/* It is facing the screen, so draw */
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/* Appropriately adjust the extent of the rectangle used to
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erase this object later */
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for (j=0; j<NumVertices; j++) {
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if (Vertices[j].X >
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ObjectToXform->EraseRect[NonDisplayedPage].Right)
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if (Vertices[j].X < SCREEN-WIDTH)
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ObjectToXform->EraseRect[NonDisplayedPage].Right =
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Vertices[j].X;
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else ObjectToXform->EraseRect[NonDisplayedPage].Right =
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SCREEN-WIDTH;
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if (Vertices[j].Y >
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ObjectToXform->EraseRect[NonDisplayedPage].Bottom)
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if (Vertices[j].Y < SCREEN-HEIGHT)
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ObjectToXform->EraseRect[NonDisplayedPage].Bottom =
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Vertices[j].Y;
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else ObjectToXform->EraseRect[NonDisplayedPage].Bottom=
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SCREEN-HEIGHT;
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if (Vertices[j].X <
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ObjectToXform->EraseRect[NonDisplayedPage].Left)
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if (Vertices[j].X > 0)
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ObjectToXform->EraseRect[NonDisplayedPage].Left =
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Vertices[j].X;
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else ObjectToXform->EraseRect[NonDisplayedPage].Left=0;
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if (Vertices[j].Y <
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ObjectToXform->EraseRect[NonDisplayedPage].Top)
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if (Vertices[j].Y > 0)
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ObjectToXform->EraseRect[NonDisplayedPage].Top =
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Vertices[j].Y;
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else ObjectToXform->EraseRect[NonDisplayedPage].Top=0;
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}
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/* See if there's any shading */
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if (FacePtr->ShadingType == 0) {
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/* No shading in effect, so just draw */
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DRAW-POLYGON(Vertices, NumVertices, FacePtr->ColorIndex, 0, 0);
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} else {
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/* Handle shading */
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/* Do ambient shading, if enabled */
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if (AmbientOn && (FacePtr->ShadingType & AMBIENT-SHADING)) {
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/* Use the ambient shading component */
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IntensityTemp = AmbientIntensity;
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} else {
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SET-INTENSITY(IntensityTemp, 0, 0, 0);
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}
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/* Do diffuse shading, if enabled */
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if (FacePtr->ShadingType & DIFFUSE-SHADING) {
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/* Calculate the unit normal for this polygon, for use in dot
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products */
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UnitNormal.X = NormalEndpoint->X - NormalStartpoint->X;
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UnitNormal.Y = NormalEndpoint->Y - NormalStartpoint->Y;
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UnitNormal.Z = NormalEndpoint->Z - NormalStartpoint->Z;
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/* Calculate the diffuse shading component for each active
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spotlight */
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for (Spot=0; Spot<MAX-SPOTS; Spot++) {
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if (SpotOn[Spot] != 0) {
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/* Spot is on, so sum, for each color component, the
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intensity, accounting for the angle of the light rays
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relative to the orientation of the polygon */
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/* Calculate cosine of angle between the light and the
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polygon normal; skip if spot is shining from behind
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the polygon */
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if ((Diffusion = DOT-PRODUCT(SpotDirectionView[Spot],
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UnitNormal)) > 0) {
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IntensityTemp.Red +=
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FixedMul(SpotIntensity[Spot].Red, Diffusion);
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IntensityTemp.Green +=
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FixedMul(SpotIntensity[Spot].Green, Diffusion);
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IntensityTemp.Blue +=
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FixedMul(SpotIntensity[Spot].Blue, Diffusion);
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}
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}
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}
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}
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/* Convert the drawing color to the desired fraction of the
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brightest possible color */
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IntensityAdjustColor(&ColorTemp, &FacePtr->FullColor,
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&IntensityTemp);
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/* Draw with the cumulative shading, converting from the general
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color representation to the best-match color index */
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DRAW-POLYGON(Vertices, NumVertices,
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ModelColorToColorIndex(&ColorTemp), 0, 0);
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}
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}
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}
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}
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</PRE>
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<!-- END CODE //-->
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<P><BR></P>
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<CENTER>
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<TABLE BORDER>
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<TR>
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<TD><A HREF="54-03.html">Previous</A></TD>
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<TD><A HREF="index.html">Table of Contents</A></TD>
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</TR>
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</CENTER>
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<hr width="90%" size="1" noshade>
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<div align="center">
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<font face="Verdana,sans-serif" size="1">Graphics Programming Black Book © 2001 Michael Abrash</font>
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</div>
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