optimization: eliminate projection division from column loop

diff --git a/src/voxscape.c b/src/voxscape.c
index e2e8f4d..940ae06 100644 (file)
--- a/src/voxscape.c
+++ b/src/voxscape.c
@@ -59,6 +59,8 @@ struct voxscape {
        unsigned int valid;
 };
 
+static int *projtab;
+
 int vox_quality = 1;
 
 struct voxscape *vox_create(int xsz, int ysz, uint8_t *himg, uint8_t *cimg)
@@ -224,7 +226,9 @@ void vox_proj(struct voxscape *vox, int fov, int znear, int zfar)
        if(!vox->slicelen) {
                if(!(vox->slicelen = iwram_sbrk(vox->nslices * sizeof *vox->slicelen))) {
                        panic(get_pc(), "vox_proj: failed to allocate slice length table (%d)\n", vox->nslices);
-                       return;
+               }
+               if(!(projtab = iwram_sbrk(vox->nslices * sizeof *projtab))) {
+                       panic(get_pc(), "vox_proj: failed to allocate projection table (%d)\n", vox->nslices);
                }
        }
 
@@ -268,6 +272,7 @@ void vox_begin(struct voxscape *vox)
                float theta = (float)vox->fov * M_PI / 360.0f;  /* half angle */
                for(i=0; i<vox->nslices; i++) {
                        vox->slicelen[i] = (int32_t)((vox->znear + i) * tan(theta) * 4.0f * 65536.0f);
+                       projtab[i] = (HSCALE << 8) / (vox->znear + i);
                }
                vox->valid |= SLICELEN;
        }
@@ -298,7 +303,8 @@ void vox_render_slice(struct voxscape *vox, int n)
                        color = last_col;
                } else {
                        hval = vox->height[offs] - vox->vheight;
-                       hval = hval * HSCALE / (vox->znear + n) + vox->horizon;
+                       /*hval = hval * HSCALE / (vox->znear + n) + vox->horizon;*/
+                       hval = ((hval * projtab[n]) >> 8) + vox->horizon;
                        if(hval > FBHEIGHT) hval = FBHEIGHT;
                        color = vox->color[offs];
                        last_offs = offs;