From 92ed513b57e4c4ccf3a413cad763278e3a8372f7 Mon Sep 17 00:00:00 2001
From: Tom Barrett <tom@tombarrett.xyz>
Date: Thu, 1 Jul 2021 17:35:12 +0200
Subject: we now use points, split up projection rotation, and added an axis

---
 src/main.zig | 214 ++++++++++++++++++++++++++++++++++++++++-------------------
 src/sdl.zig  |   5 +-
 2 files changed, 147 insertions(+), 72 deletions(-)

(limited to 'src')

diff --git a/src/main.zig b/src/main.zig
index 9a26a6c..89ce7d8 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -3,107 +3,175 @@ const matrix = @import("matrix.zig");
 const sdl = @import("sdl.zig");
 
 const Cube = struct {
-    points: [8][3]f32,
+    points: [8]Point,
+};
+
+pub const Point = struct {
+    x: f32,
+    y: f32,
+    z: f32,
 };
 
 pub fn draw_cube(instance: sdl.instance, cube: Cube) void {
-    var c = cube.points;
     sdl.draw_color(instance, 255, 255, 255, 0);
-    sdl.draw_line(instance, &c[0], &c[1]);
-    sdl.draw_line(instance, &c[0], &c[2]);
-    sdl.draw_line(instance, &c[0], &c[4]);
+    sdl.draw_line(instance, cube.points[0], cube.points[1]);
+    sdl.draw_line(instance, cube.points[0], cube.points[2]);
+    sdl.draw_line(instance, cube.points[0], cube.points[4]);
 
-    sdl.draw_line(instance, &c[7], &c[6]);
-    sdl.draw_line(instance, &c[7], &c[5]);
-    sdl.draw_line(instance, &c[7], &c[3]);
+    sdl.draw_line(instance, cube.points[7], cube.points[6]);
+    sdl.draw_line(instance, cube.points[7], cube.points[5]);
+    sdl.draw_line(instance, cube.points[7], cube.points[3]);
 
-    sdl.draw_line(instance, &c[2], &c[3]);
-    sdl.draw_line(instance, &c[4], &c[5]);
-    sdl.draw_line(instance, &c[1], &c[5]);
+    sdl.draw_line(instance, cube.points[2], cube.points[3]);
+    sdl.draw_line(instance, cube.points[4], cube.points[5]);
+    sdl.draw_line(instance, cube.points[1], cube.points[5]);
 
-    sdl.draw_line(instance, &c[6], &c[2]);
-    sdl.draw_line(instance, &c[3], &c[1]);
-    sdl.draw_line(instance, &c[4], &c[6]);
+    sdl.draw_line(instance, cube.points[6], cube.points[2]);
+    sdl.draw_line(instance, cube.points[3], cube.points[1]);
+    sdl.draw_line(instance, cube.points[4], cube.points[6]);
 }
 
-pub fn get_shifted_cube(cube: Cube, x: f32, y: f32, z: f32) Cube {
+pub fn shift_cube(cube: Cube, x: f32, y: f32, z: f32) Cube {
     var shifted_cube = Cube{ .points = undefined };
     for (cube.points) |point, i| {
-        shifted_cube.points[i][0] = point[0] + x;
-        shifted_cube.points[i][1] = point[1] + y;
-        shifted_cube.points[i][2] = point[2] + z;
+        shifted_cube.points[i].x = point.x + x;
+        shifted_cube.points[i].y = point.y + y;
+        shifted_cube.points[i].z = point.z + z;
     }
-
     return shifted_cube;
 }
 
-pub fn get_centered_cube(cube: Cube, offset: f32) Cube {
+pub fn center_cube(cube: Cube, offset: f32) Cube {
     var centered_cube = Cube{ .points = undefined };
     for (cube.points) |point, i| {
-        for (point) |dimension, j| {
-            centered_cube.points[i][j] = dimension + offset;
-        }
+        centered_cube.points[i] = center_point(point, offset);
     }
     return centered_cube;
 }
 
-pub fn get_projected_cube(cube: Cube, alpha: f32, beta: f32) Cube {
+pub fn center_point(point: Point, offset: f32) Point {
+    return Point{
+        .x = point.x + offset,
+        .y = point.y + offset,
+        .z = 0,
+    };
+}
+
+pub fn rotate_cube(cube: Cube, alpha: f32, beta: f32) Cube {
+    var rotated_cube = Cube{ .points = undefined };
+
+    var a = matrix.new(
+        3,
+        3,
+        &[_]f32{
+            1, 0,            0,
+            0, @cos(alpha),  @sin(alpha),
+            0, -@sin(alpha), @cos(alpha),
+        },
+    );
+
+    var b = matrix.new(
+        3,
+        3,
+        &[_]f32{
+            @cos(beta), 0, -@sin(beta),
+            0,          1, 0,
+            @sin(beta), 0, @cos(beta),
+        },
+    );
+
+    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];
+    }
+
+    return rotated_cube;
+}
+
+pub fn project_cube(cube: Cube) Cube {
     var projected_cube = Cube{ .points = undefined };
 
-    var ax = [_]f32{
-        1, 0,            0,
-        0, @cos(alpha),  @sin(alpha),
-        0, -@sin(alpha), @cos(alpha),
-    };
-    var a = matrix.new(3, 3, &ax);
+    for (cube.points) |point, i| {
+        projected_cube.points[i] = project_point(point);
+    }
 
-    var bx = [_]f32{
-        @cos(beta), 0, -@sin(beta),
-        0,          1, 0,
-        @sin(beta), 0, @cos(beta),
-    };
-    var b = matrix.new(3, 3, &bx);
+    return projected_cube;
+}
 
+pub fn project_point(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;
 
-    for (cube.points) |point, i| {
-        var p = point;
-        var x = matrix.multiply(c, matrix.multiply(matrix.multiply(a, b), matrix.new(3, 1, &p))).x.items;
-        projected_cube.points[i][0] = x[0];
-        projected_cube.points[i][1] = x[1];
-    }
+    var projected_point = Point{
+        .x = m[0],
+        .y = m[1],
+        .z = m[2],
+    };
 
-    return projected_cube;
+    return projected_point;
 }
 
-pub fn get_scaled_cube(cube: Cube, scale: f32) Cube {
+pub fn scale_cube(cube: Cube, scale: f32) Cube {
     var scaled_cube = Cube{ .points = undefined };
     for (cube.points) |point, i| {
-        for (point) |dimension, j| {
-            scaled_cube.points[i][j] = dimension * scale;
-        }
+        scaled_cube.points[i].x = point.x * scale;
+        scaled_cube.points[i].y = point.y * scale;
+        scaled_cube.points[i].z = point.z * scale;
     }
     return scaled_cube;
 }
 
+pub fn draw_axis(instance: sdl.instance) void {
+    var o = center_point(
+        project_point(Point{ .x = 00, .y = 00, .z = 00 }),
+        250,
+    );
+    var x = center_point(
+        project_point(Point{ .x = 50, .y = 00, .z = 00 }),
+        250,
+    );
+    var y = center_point(
+        project_point(Point{ .x = 00, .y = 50, .z = 00 }),
+        250,
+    );
+    var z = center_point(
+        project_point(Point{ .x = 00, .y = 00, .z = 50 }),
+        250,
+    );
+
+    sdl.draw_color(instance, 255, 0, 0, 0);
+    sdl.draw_line(instance, o, x);
+
+    sdl.draw_color(instance, 0, 255, 0, 0);
+    sdl.draw_line(instance, o, y);
+
+    sdl.draw_color(instance, 0, 0, 255, 0);
+    sdl.draw_line(instance, o, z);
+}
+
 pub fn main() anyerror!void {
     var instance = sdl.init();
 
     const unit_cube = Cube{
-        .points = [8][3]f32{
-            [3]f32{ 01, 01, 01 },
-            [3]f32{ 01, 01, -1 },
-            [3]f32{ 01, -1, 01 },
-            [3]f32{ 01, -1, -1 },
-            [3]f32{ -1, 01, 01 },
-            [3]f32{ -1, 01, -1 },
-            [3]f32{ -1, -1, 01 },
-            [3]f32{ -1, -1, -1 },
+        .points = [8]Point{
+            Point{ .x = 01, .y = 01, .z = 01 },
+            Point{ .x = 01, .y = 01, .z = -1 },
+            Point{ .x = 01, .y = -1, .z = 01 },
+            Point{ .x = 01, .y = -1, .z = -1 },
+            Point{ .x = -1, .y = 01, .z = 01 },
+            Point{ .x = -1, .y = 01, .z = -1 },
+            Point{ .x = -1, .y = -1, .z = 01 },
+            Point{ .x = -1, .y = -1, .z = -1 },
         },
     };
 
@@ -123,28 +191,34 @@ pub fn main() anyerror!void {
         sdl.draw_color(instance, 0, 0, 0, 0);
         sdl.clear(instance);
 
-        var cube = get_projected_cube(unit_cube, alpha, beta);
-        cube = get_scaled_cube(cube, 50);
-        cube = get_centered_cube(cube, 250);
+        var cube = rotate_cube(unit_cube, alpha, beta);
+        cube = scale_cube(cube, 50);
+        cube = project_cube(cube);
+        cube = center_cube(cube, 250);
         draw_cube(instance, cube);
 
-        cube = get_projected_cube(unit_cube, alpha + 90, beta + 90);
-        cube = get_scaled_cube(cube, 25);
-        cube = get_centered_cube(cube, 250);
+        cube = rotate_cube(unit_cube, alpha + 90, beta + 90);
+        cube = scale_cube(cube, 25);
+        cube = project_cube(cube);
+        cube = center_cube(cube, 250);
         draw_cube(instance, cube);
 
-        cube = get_shifted_cube(unit_cube, 5, 0, 0);
-        cube = get_projected_cube(cube, alpha, beta);
-        cube = get_scaled_cube(cube, 25);
-        cube = get_centered_cube(cube, 250);
+        cube = shift_cube(unit_cube, 5, 0, 0);
+        cube = rotate_cube(cube, 2 * alpha, 2 * beta);
+        cube = scale_cube(cube, 25);
+        cube = project_cube(cube);
+        cube = center_cube(cube, 250);
         draw_cube(instance, cube);
 
-        cube = get_shifted_cube(unit_cube, -5, 0, 0);
-        cube = get_projected_cube(cube, alpha, beta);
-        cube = get_scaled_cube(cube, 25);
-        cube = get_centered_cube(cube, 250);
+        cube = shift_cube(unit_cube, -5, 0, 0);
+        cube = rotate_cube(cube, 2 * alpha, 2 * beta);
+        cube = scale_cube(cube, 25);
+        cube = project_cube(cube);
+        cube = center_cube(cube, 250);
         draw_cube(instance, cube);
 
+        draw_axis(instance);
+
         beta += 0.01;
         alpha += 0.01;
 
diff --git a/src/sdl.zig b/src/sdl.zig
index c7b9906..b84bbfb 100644
--- a/src/sdl.zig
+++ b/src/sdl.zig
@@ -1,5 +1,6 @@
 const std = @import("std");
 const sdl = @cImport(@cInclude("SDL2/SDL.h"));
+const Point = @import("main.zig").Point;
 
 pub const instance = struct {
     renderer: ?*sdl.SDL_Renderer,
@@ -29,8 +30,8 @@ pub fn init() instance {
     };
 }
 
-pub fn draw_line(i: instance, p1: []f32, p2: []f32) void {
-    _ = sdl.SDL_RenderDrawLineF(i.renderer, p1[0], p1[1], p2[0], p2[1]);
+pub fn draw_line(i: instance, p1: Point, p2: Point) void {
+    _ = sdl.SDL_RenderDrawLineF(i.renderer, p1.x, p1.y, p2.x, p2.y);
 }
 
 pub fn delay(t: u32) void {
-- 
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