Add plasma effect showcase

showcase/build.zig

@@ -6,6 +6,7 @@ const root = @import("root");
 const carts = .{
     .{ "zeroman", @import("zeroman") },
     .{ "blobs", @import("blobs") },
+    .{ "plasma", @import("plasma") },
     .{ "metalgear_timer", @import("metalgear_timer") },
 };
 

showcase/build.zig.zon

@@ -12,6 +12,7 @@
         // Carts go here
         .zeroman = .{ .path = "carts/zeroman" },
         .blobs = .{ .path = "carts/blobs" },
+        .plasma = .{ .path = "carts/plasma" },
         .metalgear_timer = .{ .path = "carts/metalgear-timer" },
     },
     .paths = .{

showcase/carts/plasma/build.zig

@@ -0,0 +1,19 @@
+const std = @import("std");
+const sycl_badge = @import("sycl_badge");
+
+pub const author_name = "Fabio Arnold";
+pub const author_handle = "fabioarnold";
+pub const cart_title = "plasma";
+pub const description = "Plasma effect - computes plasma blobs and cycles their hue";
+
+pub fn build(b: *std.Build) void {
+    const optimize = b.standardOptimizeOption(.{});
+    const sycl_badge_dep = b.dependency("sycl_badge", .{});
+
+    const cart = sycl_badge.add_cart(sycl_badge_dep, b, .{
+        .name = "plasma",
+        .optimize = optimize,
+        .root_source_file = b.path("src/plasma.zig"),
+    });
+    cart.install(b);
+}

showcase/carts/plasma/build.zig.zon

@@ -0,0 +1,12 @@
+.{
+    .name = "plasma",
+    .version = "0.0.0",
+    .dependencies = .{
+        .sycl_badge = .{ .path = "../../.." },
+    },
+    .paths = .{
+        "build.zig",
+        "build.zig.zon",
+        "src",
+    },
+}

showcase/carts/plasma/src/plasma.zig

@@ -0,0 +1,99 @@
+const std = @import("std");
+const cart = @import("cart-api");
+const gfx = @import("gfx");
+
+export fn start() void {}
+
+export fn update() void {
+    updatePlasma();
+}
+
+const hue_colors = init_hue_colors: {
+    var initial_hue_colors: [256]cart.DisplayColor = undefined;
+    for (0..initial_hue_colors.len) |i| {
+        const fi: f32 = @floatFromInt(i);
+        const rgb = hsv2rgb(fi * 360.0 / 256.0, 1, 1);
+        initial_hue_colors[i] = .{
+            .r = @intFromFloat(rgb.r * 31),
+            .g = @intFromFloat(rgb.g * 63),
+            .b = @intFromFloat(rgb.b * 31),
+        };
+    }
+    break :init_hue_colors initial_hue_colors;
+};
+
+var plasma_buffer = init_plasma_buffer: {
+    @setEvalBranchQuota(100000);
+    var initial_plasma_buffer: [cart.framebuffer.len]u8 = undefined;
+    var y: usize = 0;
+    while (y < cart.screen_height) : (y += 1) {
+        var x: usize = 0;
+        while (x < cart.screen_width) : (x += 1) {
+            const fx: f32 = @floatFromInt(x);
+            const fy: f32 = @floatFromInt(y);
+            var value: f32 = @sin(fx / 16.0);
+            value += @sin(fy / 8.0);
+            value += @sin((fx + fy) / 16.0);
+            value += @sin(@sqrt(fx * fx + fy * fy) / 8.0);
+            // shift range from -4 .. 4 to 0 .. 255
+            value = std.math.clamp((value + 4) * 32, 0, 255);
+            initial_plasma_buffer[y * cart.screen_width + x] = @intFromFloat(value);
+        }
+    }
+    break :init_plasma_buffer initial_plasma_buffer;
+};
+
+fn updatePlasma() void {
+    for (0..cart.framebuffer.len) |i| {
+        plasma_buffer[i] +%= 2;
+        cart.framebuffer[i] = hue_colors[plasma_buffer[i]];
+    }
+}
+
+const RGB = struct {
+    r: f32,
+    g: f32,
+    b: f32,
+};
+
+pub fn hsv2rgb(h: f32, s: f32, v: f32) RGB {
+    const c = v * s;
+    const x = c * (1 - @abs(@mod(h / 60.0, 2) - 1));
+    const m = v - c;
+
+    var r: f32 = 0.0;
+    var g: f32 = 0.0;
+    var b: f32 = 0.0;
+
+    if (h < 60.0) {
+        r = c;
+        g = x;
+        b = 0.0;
+    } else if (h < 120.0) {
+        r = x;
+        g = c;
+        b = 0.0;
+    } else if (h < 180.0) {
+        r = 0.0;
+        g = c;
+        b = x;
+    } else if (h < 240.0) {
+        r = 0.0;
+        g = x;
+        b = c;
+    } else if (h < 300.0) {
+        r = x;
+        g = 0.0;
+        b = c;
+    } else {
+        r = c;
+        g = 0.0;
+        b = x;
+    }
+
+    return RGB{
+        .r = r + m,
+        .g = g + m,
+        .b = b + m,
+    };
+}