add blue gradient background

in_one_weekend/src/main.zig

@@ -1,70 +1,107 @@
 const std = @import("std");
-const sdl = @cImport({
-    @cInclude("SDL.h");
-});
+const print = std.debug.print;
+const sdl = @import("sdl.zig");
+const vec3 = @import("vec3.zig");
+const Vec3 = vec3.Vec3;
+const Color = vec3.Color;
+const Point3 = vec3.Point3;
+const Ray = @import("ray.zig").Ray;
 
 // From: https://github.com/Nelarius/weekend-raytracer-zig/blob/master/src/main.zig
 // See https://github.com/zig-lang/zig/issues/565
 // SDL_video.h:#define SDL_WINDOWPOS_UNDEFINED         SDL_WINDOWPOS_UNDEFINED_DISPLAY(0)
 // SDL_video.h:#define SDL_WINDOWPOS_UNDEFINED_DISPLAY(X)  (SDL_WINDOWPOS_UNDEFINED_MASK|(X))
 // SDL_video.h:#define SDL_WINDOWPOS_UNDEFINED_MASK    0x1FFF0000u
-const SDL_WINDOWPOS_UNDEFINED = @bitCast(c_int, sdl.SDL_WINDOWPOS_UNDEFINED_MASK);
+const SDL_WINDOWPOS_UNDEFINED = @bitCast(c_int, sdl.c.SDL_WINDOWPOS_UNDEFINED_MASK);
 
-const win_width = 640;
-const win_height = 320;
 const fps = 60;
 
+fn rayColor(ray: Ray) Color {
+    const unitDirection = vec3.unitVector(ray.direction);
+    const t = 0.5 * (unitDirection.y + 1.0);
+    const white = Color{ .x = 1.0, .y = 1.0, .z = 1.0 };
+    const blue = Color{ .x = 0.5, .y = 0.7, .z = 1.0 };
+    return white.mul(1.0 - t).add(blue.mul(t));
+}
+
 pub fn main() anyerror!void {
-    if (sdl.SDL_Init(sdl.SDL_INIT_VIDEO) != 0) {
-        std.log.err("Unable to initialize SDL: {}", .{sdl.SDL_GetError()});
+    if (sdl.c.SDL_Init(sdl.c.SDL_INIT_VIDEO) != 0) {
+        std.log.err("Unable to initialize SDL: {}", .{sdl.c.SDL_GetError()});
         return error.SDLInitializationFailed;
     }
-    defer sdl.SDL_Quit();
+    defer sdl.c.SDL_Quit();
 
-    const window = sdl.SDL_CreateWindow("Raytracing in One Weekend", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, win_width, win_height, sdl.SDL_WINDOW_OPENGL) orelse {
-        std.log.err("Unable to create window: {}", .{sdl.SDL_GetError()});
+    // Image
+    const aspectRatio: f32 = 16.0 / 9.0;
+    const imageWidth = 400;
+    const imageHeight = @floatToInt(usize, imageWidth / aspectRatio);
+
+    // Camera
+    const viewportHeight = 2.0;
+    const viewportWidth = @floatToInt(usize, viewportHeight * aspectRatio);
+    const focalLength = 1.0;
+
+    const origin = Vec3{};
+    const horizontal = Vec3{ .x = viewportWidth };
+    const vertical = Vec3{ .y = viewportHeight };
+    const lowerLeftCorner = origin.sub(horizontal.div(2)).sub(vertical.div(2)).sub(Vec3{ .z = focalLength });
+
+    const window = sdl.c.SDL_CreateWindow(
+        "Raytracing in One Weekend",
+        SDL_WINDOWPOS_UNDEFINED,
+        SDL_WINDOWPOS_UNDEFINED,
+        imageWidth,
+        imageHeight,
+        sdl.c.SDL_WINDOW_OPENGL
+    ) orelse {
+        std.log.err("Unable to create window: {}", .{sdl.c.SDL_GetError()});
         return error.SDLInitializationFailed;
     };
 
-    const surface = sdl.SDL_GetWindowSurface(window) orelse {
-        std.log.err("Unable to get window surface: {}", .{sdl.SDL_GetError()});
+    const surface = sdl.c.SDL_GetWindowSurface(window) orelse {
+        std.log.err("Unable to get window surface: {}", .{sdl.c.SDL_GetError()});
         return error.SDLInitializationFailed;
     };
 
     {
-        _ = sdl.SDL_LockSurface(surface);
+        _ = sdl.c.SDL_LockSurface(surface);
 
-        var h: usize = 0;
-        while (h < win_height) {
-            var w: usize = 0;
-            while (w < win_width) {
-                // std.log.info("w = {}, h = {}", .{ w, h });
-                const index = w * 4 + h * @intCast(usize, surface.*.pitch);
-                const target_pixel = @ptrToInt(surface.*.pixels) + index;
-                @intToPtr(*u32, target_pixel).* = 0xffffffff;
-                w += 1;
+        var j: usize = 0;
+        while (j < imageHeight) {
+            var i: usize = 0;
+            while (i < imageWidth) {
+                const u = @intToFloat(f32, i) / @intToFloat(f32, (imageWidth - 1));
+                // SDL coordinate system is flipped compared to the raytracer
+                const v = @intToFloat(f32, (imageHeight - 1) - j) / @intToFloat(f32, (imageHeight - 1));
+                const r = Ray{
+                    .origin = origin,
+                    .direction = lowerLeftCorner.add(horizontal.mul(u).add(vertical.mul(v).sub(origin))),
+                };
+                const pixelColor = rayColor(r);
+                sdl.setSurfacePixel(surface, i, j, pixelColor);
+                i += 1;
             }
-            h += 1;
+            j += 1;
         }
-        defer sdl.SDL_UnlockSurface(surface);
+        defer sdl.c.SDL_UnlockSurface(surface);
     }
 
-    if (sdl.SDL_UpdateWindowSurface(window) != 0) {
-        std.log.err("Error updating window surface: {}", .{sdl.SDL_GetError()});
+    if (sdl.c.SDL_UpdateWindowSurface(window) != 0) {
+        std.log.err("Error updating window surface: {}", .{sdl.c.SDL_GetError()});
         return error.SDLUpdateWindowFailed;
     }
 
     var running = true;
     while (running) {
-        var event: sdl.SDL_Event = undefined;
-        while (sdl.SDL_PollEvent(&event) != 0) {
+        var event: sdl.c.SDL_Event = undefined;
+        while (sdl.c.SDL_PollEvent(&event) != 0) {
             switch (event.@"type") {
-                sdl.SDL_QUIT => {
+                sdl.c.SDL_QUIT => {
                     running = false;
                 },
                 else => {},
             }
         }
-        sdl.SDL_Delay(1000 / fps);
+        sdl.c.SDL_Delay(1000 / fps);
     }
 }

in_one_weekend/src/ray.zig

@@ -0,0 +1,11 @@
+const Vec3 = @import("vec3.zig").Vec3;
+const Point3 = @import("vec3.zig").Point3;
+
+pub const Ray = struct {
+    origin: Point3,
+    direction: Vec3,
+
+    pub fn at(t: f32) Point3 {
+        return origin.add(direction.mul(t));
+    }
+};

in_one_weekend/src/vec3.zig

@@ -0,0 +1,78 @@
+const math = @import("std").math;
+
+pub const Vec3 = packed struct {
+    x: f32 = 0.0,
+    y: f32 = 0.0,
+    z: f32 = 0.0,
+
+    pub fn add(u: Vec3, v: Vec3) Vec3 {
+        return Vec3{
+            .x = u.x + v.x,
+            .y = u.y + v.y,
+            .z = u.z + v.z,
+        };
+    }
+
+    pub fn sub(u: Vec3, v: Vec3) Vec3 {
+        return Vec3{
+            .x = u.x - v.x,
+            .y = u.y - v.y,
+            .z = u.z - v.z,
+        };
+    }
+
+    pub fn mul(self: Vec3, scalar: f32) Vec3 {
+        return Vec3{
+            .x = self.x * scalar,
+            .y = self.y * scalar,
+            .z = self.z * scalar,
+        };
+    }
+
+    pub fn div(self: Vec3, scalar: f32) Vec3 {
+        return Vec3{
+            .x = self.x / scalar,
+            .y = self.y / scalar,
+            .z = self.z / scalar,
+        };
+    }
+
+    pub fn length(self: Vec3) f32 {
+        return math.sqrt(self.x * self.x + self.y * self.y + self.z * self.z);
+    }
+
+    pub fn dot(u: Vec3, v: Vec3) f32 {
+        return u.x * v.x + u.y * v.y + u.z * v.z;
+    }
+
+    pub fn cross(u: Vec3, v: Vec3) Vec3 {
+        return Vec3{
+            .x = u.y * v.z - u.z * v.y,
+            .y = u.z * v.x - u.x * v.z,
+            .z = u.x * v.y - u.y * v.x,
+        };
+    }
+
+    // pub fn unit_vector() Vec3 {
+    //     return
+    // }
+};
+
+pub fn unitVector(vec: Vec3) Vec3 {
+    return vec.div(vec.length());
+}
+
+pub const Point3 = Vec3;
+pub const Color = Vec3;
+
+const assert = @import("std").debug.assert;
+
+fn assert_cmp(actual: f32, expected: f32) void {
+    const epsilon: f32 = 1e-5;
+    assert(math.fabs(actual - expected) < epsilon);
+}
+
+test "Vec3.length" {
+    const v = Vec3{ .x = 1.0, .y = 1.0, .z = 1.0 };
+    assert_cmp(v.length(), 1.7320508);
+}