From b71d60ad473cf4771dc845c0ce0096bfc7ce8d6d Mon Sep 17 00:00:00 2001
From: Tom Barrett <tom@tombarrett.xyz>
Date: Fri, 2 Jul 2021 17:36:23 +0200
Subject: now i properly use dynamic memory, athough its very inefficient

---
 src/main.zig   | 85 +++++++++++++++++++++++++++++++++-------------------------
 src/matrix.zig | 11 ++++----
 2 files changed, 54 insertions(+), 42 deletions(-)

(limited to 'src')

diff --git a/src/main.zig b/src/main.zig
index 89ce7d8..ffaf130 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,6 +1,7 @@
 const std = @import("std");
 const matrix = @import("matrix.zig");
 const sdl = @import("sdl.zig");
+const ArenaAllocator = std.heap.ArenaAllocator;
 
 const Cube = struct {
     points: [8]Point,
@@ -57,10 +58,19 @@ pub fn center_point(point: Point, offset: f32) Point {
     };
 }
 
-pub fn rotate_cube(cube: Cube, alpha: f32, beta: f32) Cube {
+pub fn rotate_cube(arena: *ArenaAllocator, cube: Cube, alpha: f32, beta: f32) Cube {
     var rotated_cube = Cube{ .points = undefined };
 
+    for (cube.points) |point, i| {
+        rotated_cube.points[i] = rotate_point(arena, point, alpha, beta);
+    }
+
+    return rotated_cube;
+}
+
+pub fn rotate_point(arena: *ArenaAllocator, point: Point, alpha: f32, beta: f32) Point {
     var a = matrix.new(
+        arena,
         3,
         3,
         &[_]f32{
@@ -71,6 +81,7 @@ pub fn rotate_cube(cube: Cube, alpha: f32, beta: f32) Cube {
     );
 
     var b = matrix.new(
+        arena,
         3,
         3,
         &[_]f32{
@@ -80,45 +91,43 @@ pub fn rotate_cube(cube: Cube, alpha: f32, beta: f32) Cube {
         },
     );
 
-    for (cube.points) |point, i| {
-        var m = matrix.multiply(
-            matrix.multiply(a, b),
-            matrix.new(3, 1, &[3]f32{ point.x, point.y, point.z }),
-        ).x.items;
-        rotated_cube.points[i].x = m[0];
-        rotated_cube.points[i].y = m[1];
-        rotated_cube.points[i].z = m[2];
-    }
+    var m = matrix.multiply(
+        arena,
+        matrix.multiply(arena, a, b),
+        matrix.new(arena, 3, 1, &[3]f32{ point.x, point.y, point.z }),
+    );
 
-    return rotated_cube;
+    return Point{
+        .x = m.x.items[0],
+        .y = m.x.items[1],
+        .z = m.x.items[2],
+    };
 }
 
-pub fn project_cube(cube: Cube) Cube {
+pub fn project_cube(arena: *ArenaAllocator, cube: Cube) Cube {
     var projected_cube = Cube{ .points = undefined };
 
     for (cube.points) |point, i| {
-        projected_cube.points[i] = project_point(point);
+        projected_cube.points[i] = project_point(arena, point);
     }
 
     return projected_cube;
 }
 
-pub fn project_point(p: Point) Point {
+pub fn project_point(arena: *ArenaAllocator, p: Point) Point {
     var cx = [_]f32{
         1, 0, 0,
         0, 1, 0,
         0, 0, 0,
     };
-    var c = matrix.new(3, 3, &cx);
-    var m = matrix.multiply(c, matrix.new(3, 1, &[3]f32{ p.x, p.y, p.z })).x.items;
+    var c = matrix.new(arena, 3, 3, &cx);
+    var m = matrix.multiply(arena, c, matrix.new(arena, 3, 1, &[3]f32{ p.x, p.y, p.z }));
 
-    var projected_point = Point{
-        .x = m[0],
-        .y = m[1],
-        .z = m[2],
+    return Point{
+        .x = m.x.items[0],
+        .y = m.x.items[1],
+        .z = m.x.items[2],
     };
-
-    return projected_point;
 }
 
 pub fn scale_cube(cube: Cube, scale: f32) Cube {
@@ -131,21 +140,21 @@ pub fn scale_cube(cube: Cube, scale: f32) Cube {
     return scaled_cube;
 }
 
-pub fn draw_axis(instance: sdl.instance) void {
+pub fn draw_axis(arena: *ArenaAllocator, instance: sdl.instance) void {
     var o = center_point(
-        project_point(Point{ .x = 00, .y = 00, .z = 00 }),
+        project_point(arena, Point{ .x = 00, .y = 00, .z = 00 }),
         250,
     );
     var x = center_point(
-        project_point(Point{ .x = 50, .y = 00, .z = 00 }),
+        project_point(arena, Point{ .x = 50, .y = 00, .z = 00 }),
         250,
     );
     var y = center_point(
-        project_point(Point{ .x = 00, .y = 50, .z = 00 }),
+        project_point(arena, Point{ .x = 00, .y = 50, .z = 00 }),
         250,
     );
     var z = center_point(
-        project_point(Point{ .x = 00, .y = 00, .z = 50 }),
+        project_point(arena, Point{ .x = 00, .y = 00, .z = 50 }),
         250,
     );
 
@@ -178,6 +187,7 @@ pub fn main() anyerror!void {
     var beta: f32 = 0;
     var alpha: f32 = 0;
     while (true) {
+        var arena = ArenaAllocator.init(std.heap.page_allocator);
         var event = sdl.get_event();
         if (event.mode == sdl.modes.quit) {
             break;
@@ -191,37 +201,38 @@ pub fn main() anyerror!void {
         sdl.draw_color(instance, 0, 0, 0, 0);
         sdl.clear(instance);
 
-        var cube = rotate_cube(unit_cube, alpha, beta);
+        draw_axis(&arena, instance);
+
+        var cube = rotate_cube(&arena, unit_cube, alpha, beta);
         cube = scale_cube(cube, 50);
-        cube = project_cube(cube);
+        cube = project_cube(&arena, cube);
         cube = center_cube(cube, 250);
         draw_cube(instance, cube);
 
-        cube = rotate_cube(unit_cube, alpha + 90, beta + 90);
+        cube = rotate_cube(&arena, unit_cube, alpha + 90, beta + 90);
         cube = scale_cube(cube, 25);
-        cube = project_cube(cube);
+        cube = project_cube(&arena, cube);
         cube = center_cube(cube, 250);
         draw_cube(instance, cube);
 
         cube = shift_cube(unit_cube, 5, 0, 0);
-        cube = rotate_cube(cube, 2 * alpha, 2 * beta);
+        cube = rotate_cube(&arena, cube, 2 * alpha, 2 * beta);
         cube = scale_cube(cube, 25);
-        cube = project_cube(cube);
+        cube = project_cube(&arena, cube);
         cube = center_cube(cube, 250);
         draw_cube(instance, cube);
 
         cube = shift_cube(unit_cube, -5, 0, 0);
-        cube = rotate_cube(cube, 2 * alpha, 2 * beta);
+        cube = rotate_cube(&arena, cube, 2 * alpha, 2 * beta);
         cube = scale_cube(cube, 25);
-        cube = project_cube(cube);
+        cube = project_cube(&arena, cube);
         cube = center_cube(cube, 250);
         draw_cube(instance, cube);
 
-        draw_axis(instance);
-
         beta += 0.01;
         alpha += 0.01;
 
+        arena.deinit();
         sdl.present(instance);
         sdl.delay(10);
     }
diff --git a/src/matrix.zig b/src/matrix.zig
index eaf9685..e566bc4 100644
--- a/src/matrix.zig
+++ b/src/matrix.zig
@@ -1,5 +1,6 @@
 const std = @import("std");
 const ArrayList = std.ArrayList;
+const ArenaAllocator = std.heap.ArenaAllocator;
 
 const matrix = struct {
     h: usize,
@@ -7,11 +8,11 @@ const matrix = struct {
     x: ArrayList(f32),
 };
 
-pub fn new(h: usize, w: usize, x: []f32) matrix {
+pub fn new(arena: *ArenaAllocator, h: usize, w: usize, x: []f32) matrix {
     var m = matrix{
         .h = h,
         .w = w,
-        .x = ArrayList(f32).init(std.heap.page_allocator),
+        .x = ArrayList(f32).init(&arena.allocator),
     };
 
     var i: usize = 0;
@@ -37,8 +38,8 @@ pub fn dot(a: []f32, b: []f32, len: usize, step: usize) f32 {
     return x;
 }
 
-pub fn multiply(a: matrix, b: matrix) matrix {
-    var x = ArrayList(f32).init(std.heap.page_allocator);
+pub fn multiply(arena: *ArenaAllocator, a: matrix, b: matrix) matrix {
+    var x = ArrayList(f32).init(&arena.allocator);
     var i: usize = 0;
     var k: usize = 0;
 
@@ -50,5 +51,5 @@ pub fn multiply(a: matrix, b: matrix) matrix {
         k += a.w;
     }
 
-    return new(a.h, b.w, x.items);
+    return new(arena, a.h, b.w, x.items);
 }
-- 
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