From 276804c4b8db837e238880d4bc668ed6c65dd42a Mon Sep 17 00:00:00 2001
From: tslil clingman <>
Date: Mon, 20 Sep 2021 21:17:01 -0400
Subject: Corrected rendering bug

---
 src/constants.zig |  4 ++--
 src/player.zig    | 22 ++++++++++++----------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/src/constants.zig b/src/constants.zig
index d363af5..1ca0c4f 100644
--- a/src/constants.zig
+++ b/src/constants.zig
@@ -18,8 +18,8 @@
 pub const ScreenWidth: f32 = 1024;
 pub const ScreenHeight: f32 = 768;
 
-pub const PlaneWidth = 640;
-pub const PlaneHeight = 480;
+pub const PlaneWidth = 320;
+pub const PlaneHeight = 240;
 
 pub const HFact = ScreenWidth / PlaneWidth;
 pub const VFact = ScreenHeight / PlaneHeight;
diff --git a/src/player.zig b/src/player.zig
index 992ef69..98f0b47 100644
--- a/src/player.zig
+++ b/src/player.zig
@@ -355,6 +355,7 @@ pub fn Player(PlaneWidth: f32, PlaneHeight: f32) type {
                             // 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;
+                            if (texfrac == 1) texfrac = 0.9999; // i think this caused a crash at one point
                             const texstrip = @floatToInt(c_uint, constants.TextureDim * texfrac);
 
                             // which texture index?
@@ -362,25 +363,26 @@ pub fn Player(PlaneWidth: f32, PlaneHeight: f32) type {
 
                             // height of a unit-height wall at this distance
                             const nominal_length = PlaneDist / distance;
+                            const inv_nom_len = distance / PlaneDist;
 
                             // now we have what we need to draw the wall, and
                             // update the z-buffer
                             const constrained_top = std.math.min(top, PlaneHeight - 1);
-                            var y = @floatToInt(i32, constrained_top);
-                            var span = top - constrained_top;
-                            while (y > @floatToInt(i32, highest_point)) : ({
-                                y -= 1;
-                                span += 1;
+                            var zb_y = @floatToInt(i32, constrained_top);
+                            var pix_y = @floatToInt(usize, std.math.ceil(std.math.max(PlaneHeight - top, 0)));
+                            var texel_y = (top - constrained_top) / nominal_length;
+                            while (zb_y > @floatToInt(i32, highest_point)) : ({
+                                zb_y -= 1;
+                                pix_y += 1;
+                                texel_y += inv_nom_len;
                             }) {
-                                const texel_y_frac = std.math.modf(span / nominal_length).fpart;
-                                const ty = @floatToInt(c_uint, texel_y_frac * constants.TextureDim);
+                                const ty = @floatToInt(c_uint, std.math.modf(texel_y).fpart * constants.TextureDim);
                                 const texel = walls_image.getPixel(.{ .x = toff + texstrip, .y = ty });
 
-                                const coord_flip_y = @floatToInt(usize, PlaneHeight) - @intCast(usize, y);
-                                const pix_index = coord_flip_y * @floatToInt(usize, PlaneWidth) + col;
+                                const pix_index = pix_y * @floatToInt(usize, PlaneWidth) + col;
                                 pixels[pix_index] = texel;
 
-                                const index = @intCast(usize, col * @floatToInt(i32, PlaneHeight) + y);
+                                const index = @intCast(usize, col * @floatToInt(i32, PlaneHeight) + zb_y);
                                 self.z_buffer.set(index, distance);
                             }
                             highest_point = top;
-- 
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