1 files changed, 31 insertions, 20 deletions

diff --git a/src/raycast.zig b/src/raycast.zig
index dec6b46..6acc16b 100644
--- a/src/raycast.zig
+++ b/src/raycast.zig
@@ -27,10 +27,11 @@ pub const RenderWallFunction: type = fn (
     sprite: Sprite,
     col: i32, // which column we're in
     top: f32, // top of wall
-    length: f32,
+    draw_frac: f32,
+    length: f32, // length of slice to be drawn
     texfrac: f32,
     texture: u8, // which texture index
-) anyerror!void; // TODO: narrow this error type.
+) void;
 
 pub const Player = struct {
     pos_x: f32,
@@ -87,7 +88,7 @@ pub const Player = struct {
         map: Map,
         // the abstract the rendering call
         renderWall: RenderWallFunction,
-    ) !void {
+    ) void {
         const floor = std.math.floor;
 
         var col: i32 = 0;
@@ -133,6 +134,7 @@ pub const Player = struct {
 
             var distance: f32 = 0;
             var still_drawing = true;
+            var highest_point: f32 = 0;
             var horizontal_hit: bool = undefined;
             while (still_drawing) {
 
@@ -153,28 +155,37 @@ pub const Player = struct {
 
                 var cell = map.lookup(ipos_x, ipos_y);
 
-                // We have a wall to draw
-                if (cell.height > 0) {
-                    // before we correct the distance to be the perpedicular
-                    // distance from the plane of projection, we need to use it
-                    // to calculate the fractional part of the relevant
-                    // coordinate
+                // the correct distance is the shortest distance from the plane
+                // of projection to the point, that is, perpendicular distance
+                const perp_distance = distance * std.math.cos(self.ang - ra);
+
+                // project the top of the wall
+                const top = self.plane_height / 2 + self.plane_dist * (cell.height - self.height) / perp_distance;
+
+                // We have a wall to draw if it protrudes above what we have so far drawn
+                if (top > highest_point) {
+
+                    // did we extend beyond the top of the plane?
+                    if (top > self.plane_height) still_drawing = false;
+
+                    // compute the height of this wall
+                    const total_length = self.plane_dist * cell.height / perp_distance;
+
+                    // as well as the fraction we'll be drawing
+                    const draw_frac = std.math.min(1, (top - highest_point) / total_length);
+
+                    // we need the raw Euclidean distance to calculate the
+                    // fractional part of the relevant coordinate for texture
+                    // mapping of the walls
                     const hit_coordinate = if (horizontal_hit) distance * cosra + self.pos_x else distance * sinra + self.pos_y;
                     var texfrac = std.math.modf(hit_coordinate).fpart;
-                    // we also want to be sure that we're consistently orienting these, say clockwise
+                    // we also want to be sure that we're consistently orienting
+                    // textures, in this case clockwise
                     if ((horizontal_hit and sinra < 0) or (!horizontal_hit and cosra > 0)) texfrac = 1 - texfrac;
 
-                    // now correct the distance to be the shortest distance from
-                    // the plane to the point, that is, perpendicular distance
-                    distance *= std.math.cos(self.ang - ra);
-
-                    // project the top of the wall
-                    const top = self.plane_height / 2 + self.plane_dist * (cell.height - self.height) / distance;
-                    const height = self.plane_dist * cell.height / distance;
-
-                    try renderWall(window, sprite, col, top, height, texfrac, cell.wall_texture);
+                    renderWall(window, sprite, col, top, total_length, draw_frac, texfrac, cell.wall_texture);
 
-                    still_drawing = false;
+                    highest_point = top;
                 }
             }
         }