More efficient surface rendering!

Now, outside of sprites, every pixel on the screen is draw at most
once. Hoorah. Unfortunately things still seem to be a little slow,
perhaps its the z_buffer access or the fact that vertical floor slice
drawing is bad?

4 files changed, 78 insertions, 83 deletions

diff --git a/floors.png b/floors.png
deleted file mode 100644
index 19254e7..0000000
--- a/floors.png
+++ /dev/null
diff --git a/src/main.zig b/src/main.zig
index 218ba92..c44b5e6 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -55,7 +55,7 @@ pub fn main() !void {
     }
 
     map.cells.items[16 * 7 + 7] = level.Cell{ .height = constants.MAX_HEIGHT, .wall_texture = 1 };
-    map.cells.items[16 * 7 + 6] = level.Cell{ .height = constants.MAX_HEIGHT / 4, .wall_texture = 1, .floor_texture = 0 };
+    map.cells.items[16 * 7 + 6] = level.Cell{ .height = constants.MAX_HEIGHT / 4, .wall_texture = 1, .floor_texture = 1 };
 
     try map.objects.append(level.Object{ .pos_x = 5.5, .pos_y = 7.5, .pos_z = 1, .texture = 2, .height = 1, .width = 1 });
     try map.objects.append(level.Object{ .pos_x = 4, .pos_y = 8.5, .texture = 1, .height = 1, .width = 1 });
@@ -103,18 +103,18 @@ pub fn main() !void {
     defer objects_sprite.destroy();
 
     // Load floor image
-    var floors_image = try sf.Image.createFromFile("floors.png");
-    defer floors_image.destroy();
+    var surfaces_image = try sf.Image.createFromFile("surfaces.png");
+    defer surfaces_image.destroy();
 
-    var rendered_floors_texture = try sf.Texture.create(.{ .x = constants.PlaneWidth, .y = constants.PlaneHeight });
-    defer rendered_floors_texture.destroy();
-    rendered_floors_texture.setSmooth(false);
+    var rendered_surfaces_texture = try sf.Texture.create(.{ .x = constants.PlaneWidth, .y = constants.PlaneHeight });
+    defer rendered_surfaces_texture.destroy();
+    rendered_surfaces_texture.setSmooth(false);
 
-    var rendered_floors_sprite = try sf.Sprite.createFromTexture(rendered_floors_texture);
-    defer rendered_floors_sprite.destroy();
+    var rendered_surfaces_sprite = try sf.Sprite.createFromTexture(rendered_surfaces_texture);
+    defer rendered_surfaces_sprite.destroy();
 
-    rendered_floors_sprite.setPosition(.{ .x = 0, .y = 0 });
-    rendered_floors_sprite.setScale(.{ .x = constants.HFact, .y = constants.VFact });
+    rendered_surfaces_sprite.setPosition(.{ .x = 0, .y = 0 });
+    rendered_surfaces_sprite.setScale(.{ .x = constants.HFact, .y = constants.VFact });
 
     // Start your engines!
     //--------------------------------------------------------------------------
@@ -169,9 +169,9 @@ pub fn main() !void {
             window,
             walls_sprite,
             objects_sprite,
-            floors_image,
-            rendered_floors_texture,
-            rendered_floors_sprite,
+            surfaces_image,
+            rendered_surfaces_texture,
+            rendered_surfaces_sprite,
             map,
         );
 
diff --git a/src/raycast.zig b/src/raycast.zig
index 1b78983..2b55f49 100644
--- a/src/raycast.zig
+++ b/src/raycast.zig
@@ -114,29 +114,29 @@ pub fn Player(PlaneWidth: f32, PlaneHeight: f32) type {
             window: RenderWindow,
             walls_sprite: Sprite,
             objects_sprite: Sprite,
-            floors_image: Image,
-            rendered_floors_texture: Texture,
-            rendered_floors_sprite: Sprite,
+            surfaces_image: Image,
+            rendered_surfaces_texture: Texture,
+            rendered_surfaces_sprite: Sprite,
             map: level.Map,
         ) !void {
-            // TODO: this is wasteful -- we render the floors and draw the
-            // texture, draw over that for the walls, then change the floor
-            // texture for the tops of things and blank everywhere else, then
-            // redraw the floor texture.
-
-            // First render the floors
-            try self.renderFloorsToTexture(floors_image, rendered_floors_texture, map);
-            window.draw(rendered_floors_sprite, null);
-
-            // then reset the z_buffer
+            // Fist reset the z_buffer
             var i: usize = 0;
             while (i < self.z_buffer.len) : (i += 1) {
                 self.z_buffer.set(i, std.math.inf(f32));
             }
 
-            // then render all the walls and populate the z_buffer
-            try self.renderCells(window, walls_sprite, floors_image, rendered_floors_texture, map);
-            window.draw(rendered_floors_sprite, null);
+            var pixels = [_]Colour{Colour.fromRGBA(0, 0, 0, 0)} ** (PlaneWidth * PlaneHeight);
+
+            // then draw all the walls and populate the z_buffer, while also
+            // rendering the surfaces below the horizon to the pixel array
+            self.renderCells(window, walls_sprite, surfaces_image, map, &pixels);
+
+            // then render the ceilings to our pixel array
+            self.renderCeilingsToTexture(surfaces_image, map, &pixels);
+
+            // we're now ready to draw the surfaces
+            try rendered_surfaces_texture.updateFromPixels(&pixels, null);
+            window.draw(rendered_surfaces_sprite, null);
 
             // use the z_buffer to render sprites
             self.renderObjects(window, objects_sprite, map);
@@ -220,12 +220,10 @@ pub fn Player(PlaneWidth: f32, PlaneHeight: f32) type {
             self: *@This(),
             window: RenderWindow,
             walls_sprite: Sprite,
-            floors_image : Image,
-            rendered_floors_texture : Texture,
+            floors_image: Image,
             map: level.Map,
-        ) !void {
-            var pixels = [_]Colour{Colour.fromRGBA(0, 0, 0, 0)} ** (PlaneWidth * PlaneHeight);
-
+            pixels: []Colour,
+        ) void {
             // This is a TERRIBLE hack: for whatever reason *linearly*
             // interpolating on the direction vectors gives
             // perspective-correct-seeming walls!
@@ -279,6 +277,7 @@ pub fn Player(PlaneWidth: f32, PlaneHeight: f32) type {
                     dist_x = (self.pos_y - @intToFloat(f32, ipos_y)) * dx_for_y_step;
                 }
 
+                var top: f32 = undefined;
                 var distance: f32 = 0;
                 var still_drawing = true;
                 var highest_point: f32 = 0;
@@ -302,7 +301,7 @@ pub fn Player(PlaneWidth: f32, PlaneHeight: f32) type {
                     // Is there a wall?
                     if (cell.height > 0) {
                         // project the top of the wall
-                        var top = PlaneHeight / 2 + PlaneDist * (cell.height - self.height) / distance;
+                        top = PlaneHeight / 2 + PlaneDist * (cell.height - self.height) / distance;
 
                         // Does the wall extend above what we've draw?
                         if (top > highest_point) {
@@ -340,61 +339,60 @@ pub fn Player(PlaneWidth: f32, PlaneHeight: f32) type {
                             }
                             highest_point = top;
                         }
+                    }
 
-                        // do we potentially draw the top of this cell?
-                        if (highest_point < PlaneHeight / 2) {
-                            if (dist_y < dist_x) {
-                                distance = dist_y;
-                            } else {
-                                distance = dist_x;
-                            }
+                    // do we potentially draw the top of this cell?
+                    if (highest_point < PlaneHeight / 2) {
+                        if (dist_y < dist_x) {
+                            distance = dist_y;
+                        } else {
+                            distance = dist_x;
+                        }
 
-                            // Note: next_top can never exceed PlaneHeight / 2
-                            // in the body of the next block. If the wall is
-                            // taller than us the back edge is lower than the
-                            // front one so this check will fail as we just drew
-                            // it (or higher than it). If the wall is shorter
-                            // then the back edge is at most the horizon.
-                            const next_top = PlaneHeight / 2 + PlaneDist * (cell.height - self.height) / distance;
+                        // Note: next_top can never exceed PlaneHeight / 2
+                        // in the body of the next block. If the wall is
+                        // taller than us the back edge is lower than the
+                        // front one so this check will fail as we just drew
+                        // it (or higher than it). If the wall is shorter
+                        // then the back edge is at most the horizon.
+                        const next_top = PlaneHeight / 2 + PlaneDist * (cell.height - self.height) / distance;
 
-                            // only if we can see some part of it
-                            if (next_top > highest_point) {
-                                top = highest_point;
-                                while (top <= next_top and top < PlaneHeight / 2) : (top += 1) {
-                                    const row_dist = (self.height - cell.height) * PlaneDist / (PlaneHeight / 2 - top);
-                                    const ptop = @floatToInt(usize, top + 1);
-                                    const itop = @floatToInt(usize, PlaneHeight) - ptop;
+                        // only if we can see some part of it
+                        if (next_top > highest_point) {
+                            top = highest_point;
+                            while (top <= next_top and top < PlaneHeight / 2) : (top += 1) {
+                                const row_dist = (self.height - cell.height) * PlaneDist / (PlaneHeight / 2 - top);
+                                const ptop = @floatToInt(usize, top + 1);
+                                const itop = @floatToInt(usize, PlaneHeight) - ptop;
 
-                                    // draw the correct pixel
-                                    const sx = std.math.modf(self.pos_x + row_dist * cosra);
-                                    const sy = std.math.modf(self.pos_y + row_dist * sinra);
-                                    const toff = cell.floor_texture * @floatToInt(c_uint, constants.TextureDim);
-                                    const px = @floatToInt(c_uint, constants.TextureDim * std.math.fabs(sx.fpart));
-                                    const py = @floatToInt(c_uint, constants.TextureDim * std.math.fabs(sy.fpart));
-                                    const val = floors_image.getPixel(.{ .x = toff + px, .y = py });
-                                    pixels[itop * @floatToInt(usize, PlaneWidth) + col] = val;
+                                // draw the correct pixel
+                                const sx = std.math.modf(self.pos_x + row_dist * cosra);
+                                const sy = std.math.modf(self.pos_y + row_dist * sinra);
+                                const toff = cell.floor_texture * @floatToInt(c_uint, constants.TextureDim);
+                                const px = @floatToInt(c_uint, constants.TextureDim * std.math.fabs(sx.fpart));
+                                const py = @floatToInt(c_uint, constants.TextureDim * std.math.fabs(sy.fpart));
+                                const val = floors_image.getPixel(.{ .x = toff + px, .y = py });
+                                pixels[itop * @floatToInt(usize, PlaneWidth) + col] = val;
 
-                                    // record in the z_buffer
+                                // record in the z_buffer only if we're above the floor!
+                                if (cell.height > 0) {
                                     const index = col * @floatToInt(usize, PlaneHeight) + ptop;
                                     self.z_buffer.set(index, row_dist);
                                 }
-                                highest_point = top;
                             }
+                            highest_point = top;
                         }
                     }
                 }
             }
-            try rendered_floors_texture.updateFromPixels(&pixels, null);
         }
 
-        fn renderFloorsToTexture(
+        fn renderCeilingsToTexture(
             self: @This(),
-            floors_image: Image,
-            rendered_floors_texture: Texture,
+            surfaces_image: Image,
             map: level.Map,
-        ) !void {
-            var pixels = [_]Colour{Colour.fromRGBA(0, 0, 0, 0)} ** (PlaneWidth * PlaneHeight);
-
+            pixels: []Colour,
+        ) void {
             // Again, another TERRIBLE hack: we do the same nasty linear
             // interpolation trick and for whatever reason the floors look fine.
             const cos_first = std.math.cos(self.ang + 0.5 * FOV);
@@ -403,11 +401,9 @@ pub fn Player(PlaneWidth: f32, PlaneHeight: f32) type {
             const sin_last = std.math.sin(self.ang - 0.5 * FOV);
 
             var row: usize = 0;
-            while (row < PlaneHeight) : (row += 1) {
-                if (row == PlaneHeight / 2) continue;
-                const frow = std.math.fabs(PlaneHeight / 2 - @intToFloat(f32, row));
-                const scale = if (row < PlaneHeight / 2) constants.MAX_HEIGHT - self.height else self.height;
-                const row_dist = scale * PlaneDist / frow;
+            while (row < PlaneHeight / 2) : (row += 1) {
+                const frow = (PlaneHeight / 2 - @intToFloat(f32, row));
+                const row_dist = (constants.MAX_HEIGHT - self.height) * PlaneDist / frow;
 
                 const dx_step = row_dist * (cos_last - cos_first) / PlaneWidth;
                 const dy_step = row_dist * (sin_last - sin_first) / PlaneWidth;
@@ -430,20 +426,19 @@ pub fn Player(PlaneWidth: f32, PlaneHeight: f32) type {
                     const ix = @floatToInt(i32, sx.ipart);
                     const iy = @floatToInt(i32, sy.ipart);
 
-                    if (map.inBounds(ix, iy)) {
+                    const index = col * @floatToInt(usize, PlaneHeight) + @floatToInt(usize, PlaneHeight - 1) - row;
+                    if (map.inBounds(ix, iy) and row_dist < self.z_buffer.get(index)) {
                         const cell = map.lookup(ix, iy);
-                        const tex = if (row > PlaneHeight / 2) cell.floor_texture else cell.ceiling_texture;
-                        const toff = tex * @floatToInt(c_uint, constants.TextureDim);
+                        const toff = cell.ceiling_texture * @floatToInt(c_uint, constants.TextureDim);
                         const px = @floatToInt(c_uint, constants.TextureDim * std.math.fabs(sx.fpart));
                         const py = @floatToInt(c_uint, constants.TextureDim * std.math.fabs(sy.fpart));
 
-                        const val = floors_image.getPixel(.{ .x = toff + px, .y = py });
+                        const val = surfaces_image.getPixel(.{ .x = toff + px, .y = py });
 
                         pixels[row * @floatToInt(usize, PlaneWidth) + col] = val;
                     }
                 }
             }
-            try rendered_floors_texture.updateFromPixels(&pixels, null);
         }
     };
 }
diff --git a/surfaces.png b/surfaces.png
new file mode 100644
index 0000000..f699b8b
--- /dev/null
+++ b/surfaces.png