Use backtick code blocks for syntax highlighting
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James Gregory
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203 changed files with 26546 additions and 25801 deletions
196
69-04.md
196
69-04.md
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@ -56,118 +56,120 @@ clear success.
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**LISTING 69.1 L69-1.C**
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// Quake's recursive subdivision triangle rasterizer; draws all
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// pixels in a triangle other than the vertices by splitting an
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// edge to form a new vertex, drawing the vertex, and recursively
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// processing each of the two new triangles formed by using the
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// new vertex. Results are less accurate than from a precise
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// affine or perspective texture mapper, and drawing boundaries
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// are not identical to those of a precise polygon drawer, although
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// they are consistent between adjacent polygons drawn with this
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// technique.
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//
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// Invented and implemented by John Carmack of id Software.
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```c
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// Quake's recursive subdivision triangle rasterizer; draws all
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// pixels in a triangle other than the vertices by splitting an
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// edge to form a new vertex, drawing the vertex, and recursively
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// processing each of the two new triangles formed by using the
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// new vertex. Results are less accurate than from a precise
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// affine or perspective texture mapper, and drawing boundaries
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// are not identical to those of a precise polygon drawer, although
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// they are consistent between adjacent polygons drawn with this
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// technique.
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//
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// Invented and implemented by John Carmack of id Software.
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void D_PolysetRecursiveTriangle (int *lp1, int *lp2, int *lp3)
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{
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int *temp;
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int d;
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void D_PolysetRecursiveTriangle (int *lp1, int *lp2, int *lp3)
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{
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int *temp;
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int d;
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int new[6];
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int z;
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short *zbuf;
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int new[6];
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int z;
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short *zbuf;
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// try to find an edge that's more than one pixel long in x or y
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d = lp2[0] - lp1[0];
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if (d < -1 || d > 1)
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goto split;
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d = lp2[1] - lp1[1];
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if (d < -1 || d > 1)
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goto split;
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d = lp3[0] - lp2[0];
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if (d < -1 || d > 1)
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goto split2;
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d = lp3[1] - lp2[1];
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if (d < -1 || d > 1)
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goto split2;
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d = lp1[0] - lp3[0];
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if (d < -1 || d > 1)
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goto split3;
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d = lp1[1] - lp3[1];
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if (d < -1 || d > 1)
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{
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split3:
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// shuffle points so first edge is edge to split
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temp = lp1;
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lp1 = lp3;
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lp3 = lp2;
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lp2 = temp;
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goto split;
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}
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// try to find an edge that's more than one pixel long in x or y
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d = lp2[0] - lp1[0];
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if (d < -1 || d > 1)
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goto split;
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d = lp2[1] - lp1[1];
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if (d < -1 || d > 1)
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goto split;
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d = lp3[0] - lp2[0];
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if (d < -1 || d > 1)
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goto split2;
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d = lp3[1] - lp2[1];
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if (d < -1 || d > 1)
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goto split2;
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d = lp1[0] - lp3[0];
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if (d < -1 || d > 1)
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goto split3;
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d = lp1[1] - lp3[1];
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if (d < -1 || d > 1)
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{
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split3:
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// shuffle points so first edge is edge to split
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temp = lp1;
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lp1 = lp3;
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lp3 = lp2;
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lp2 = temp;
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goto split;
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}
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return; // no pixels left to fill in triangle
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return; // no pixels left to fill in triangle
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split2:
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// shuffle points so first edge is edge to split
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temp = lp1;
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lp1 = lp2;
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lp2 = lp3;
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lp3 = temp;
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split2:
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// shuffle points so first edge is edge to split
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temp = lp1;
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lp1 = lp2;
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lp2 = lp3;
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lp3 = temp;
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split:
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// split first edge screen x, screen y, texture s, texture t, and z
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// to form a new vertex. Lighting (index 4) is ignored; the
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// difference between interpolating lighting and using the same
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// shading for the entire triangle is unnoticeable for small
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// triangles, so we just use the lighting for the first vertex of
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// the original triangle (which was used during set-up to set
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// d_colormap, used below to look up lit texels)
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new[0] = (lp1[0] + lp2[0]) >> 1; // split screen x
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new[1] = (lp1[1] + lp2[1]) >> 1; // split screen y
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new[2] = (lp1[2] + lp2[2]) >> 1; // split texture s
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new[3] = (lp1[3] + lp2[3]) >> 1; // split texture t
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new[5] = (lp1[5] + lp2[5]) >> 1; // split z
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split:
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// split first edge screen x, screen y, texture s, texture t, and z
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// to form a new vertex. Lighting (index 4) is ignored; the
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// difference between interpolating lighting and using the same
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// shading for the entire triangle is unnoticeable for small
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// triangles, so we just use the lighting for the first vertex of
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// the original triangle (which was used during set-up to set
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// d_colormap, used below to look up lit texels)
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new[0] = (lp1[0] + lp2[0]) >> 1; // split screen x
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new[1] = (lp1[1] + lp2[1]) >> 1; // split screen y
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new[2] = (lp1[2] + lp2[2]) >> 1; // split texture s
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new[3] = (lp1[3] + lp2[3]) >> 1; // split texture t
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new[5] = (lp1[5] + lp2[5]) >> 1; // split z
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// draw the point if splitting a leading edge
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if (lp2[1] > lp1[1])
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goto nodraw;
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if ((lp2[1] == lp1[1]) && (lp2[0] < lp1[0]))
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goto nodraw;
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// draw the point if splitting a leading edge
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if (lp2[1] > lp1[1])
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goto nodraw;
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if ((lp2[1] == lp1[1]) && (lp2[0] < lp1[0]))
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goto nodraw;
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z = new[5]>>16;
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z = new[5]>>16;
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// point to the pixel's z-buffer entry, looking up the scanline start
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// address based on screen y and adding in the screen x coordinate
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zbuf = zspantable[new[1]] + new[0];
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// point to the pixel's z-buffer entry, looking up the scanline start
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// address based on screen y and adding in the screen x coordinate
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zbuf = zspantable[new[1]] + new[0];
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// draw the split vertex if it's not obscured by something nearer, as
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// indicated by the z-buffer
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if (z >= *zbuf)
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{
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int pix;
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// draw the split vertex if it's not obscured by something nearer, as
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// indicated by the z-buffer
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if (z >= *zbuf)
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{
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int pix;
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// set the z-buffer to the new pixel's distance
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*zbuf = z;
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// set the z-buffer to the new pixel's distance
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*zbuf = z;
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// get the texel from the model's skin bitmap, according to
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// the s and t texture coordinates, and translate it through
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// the lighting look-up table set according to the first
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// vertex for the original (top-level) triangle. Both s and
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// t are in 16.16 format
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pix = d_pcolormap[skintable[new[3]>>16][new[2]>>16]];
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// get the texel from the model's skin bitmap, according to
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// the s and t texture coordinates, and translate it through
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// the lighting look-up table set according to the first
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// vertex for the original (top-level) triangle. Both s and
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// t are in 16.16 format
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pix = d_pcolormap[skintable[new[3]>>16][new[2]>>16]];
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// draw the pixel, looking up the scanline start address
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// based on screen y and adding in the screen x coordinate
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d_viewbuffer[d_scantable[new[1]] + new[0]] = pix;
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}
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// draw the pixel, looking up the scanline start address
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// based on screen y and adding in the screen x coordinate
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d_viewbuffer[d_scantable[new[1]] + new[0]] = pix;
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}
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nodraw:
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// recursively draw the two new triangles we created by adding the
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// split vertex
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D_PolysetRecursiveTriangle (lp3, lp1, new);
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D_PolysetRecursiveTriangle (lp3, new, lp2);
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}
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nodraw:
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// recursively draw the two new triangles we created by adding the
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// split vertex
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D_PolysetRecursiveTriangle (lp3, lp1, new);
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D_PolysetRecursiveTriangle (lp3, new, lp2);
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}
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```
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