Added GpuTexture tied to arena like buffer

src/GpuTexture.zig

@@ -0,0 +1,137 @@
+const std = @import("std");
+const c = @import("utils.zig").c;
+const GpuAllocator = @import("GpuAllocator.zig");
+const GpuTextureFormat = @import("lib.zig").GpuTextureFormat;
+
+const TextureUsage = enum(u64) {
+    None = 0x0000000000000000,
+    CopySrc = 0x0000000000000001,
+    CopyDst = 0x0000000000000002,
+    TextureBinding = 0x0000000000000004,
+    StorageBinding = 0x0000000000000008,
+    RenderAttachment = 0x0000000000000010,
+    TransientAttachment = 0x0000000000000020,
+};
+
+raw: c.WGPUTexture,
+size: c.WGPUExtent3D,
+usage: c.WGPUTextureUsage,
+format: GpuTextureFormat,
+gloc: GpuAllocator,
+
+/// Allocates the underlying WebGPU handle and registers it to the parent GpuAllocator
+pub fn init(gloc: GpuAllocator, format: GpuTextureFormat, size: c.WGPUExtent3D, usage: std.EnumSet(TextureUsage)) !@This() {
+    var use: u64 = 0;
+    var iter = usage.iterator();
+    while (iter.next()) |flag| use |= @intFromEnum(flag);
+
+    const desc = c.WGPUTextureDescriptor{
+        .usage = use,
+        .dimension = c.WGPUTextureDimension_2D,
+        .size = size,
+        .format = @intCast(@intFromEnum(format)),
+        .mipLevelCount = 1,
+        .sampleCount = 1,
+    };
+    const raw = try gloc.allocTexture(desc);
+
+    return .{ .gloc = gloc, .raw = raw, .size = size, .format = format, .usage = use };
+}
+
+/// Unregisters from the parent GpuAllocator and cleanly destroys GPU resources
+pub fn deinit(self: @This()) void {
+    self.gloc.freeTexture(self.raw);
+}
+
+/// Native getConstMappedRange wrapper
+pub fn getConstMappedRange(self: @This(), offset: u64, size: u64) ?*const anyopaque {
+    return c.wgpuBufferGetConstMappedRange(self.raw, offset, size);
+}
+
+/// Native mapAsync wrapper
+pub fn mapAsync(
+    self: @This(),
+    mode: c.WGPUMapMode,
+    offset: u64,
+    size: u64,
+    callback_info: c.WGPUBufferMapCallbackInfo,
+) void {
+    _ = c.wgpuBufferMapAsync(self.raw, mode, offset, size, callback_info);
+}
+
+/// Native unmap wrapper
+pub fn unmap(self: @This()) void {
+    c.wgpuBufferUnmap(self.raw);
+}
+
+/// CPU to GPU.
+pub fn load(
+    self: @This(),
+    T: type,
+    data: []const T,
+) !void {
+    const bytes = data.len * @sizeOf(T);
+
+    if (bytes == self.size) {
+        // Aligned path: direct download
+        c.wgpuQueueWriteBuffer(self.gloc.device.queue, self.raw, 0, data.ptr, self.size);
+    } else {
+        // Unaligned path: Split the write into an aligned chunk and a padded remainder
+        // to support arbitrary lengths without any allocations or large stack arrays.
+        const aligned_part = (bytes / 4) * 4;
+        if (aligned_part > 0) {
+            c.wgpuQueueWriteBuffer(self.gloc.device.queue, self.raw, 0, data.ptr, aligned_part);
+        }
+
+        var remainder_buf: [4]u8 = .{ 0, 0, 0, 0 };
+        const data_bytes = std.mem.sliceAsBytes(data);
+        @memcpy(remainder_buf[0 .. bytes - aligned_part], data_bytes[aligned_part..bytes]);
+
+        c.wgpuQueueWriteBuffer(self.gloc.device.queue, self.raw, aligned_part, &remainder_buf, 4);
+    }
+}
+
+pub fn read(self: @This(), alloc: std.mem.Allocator, T: type) ![]T {
+    const out = try alloc.alloc(T, @divExact(self.size, @sizeOf(T)));
+
+    const staging = try init(
+        self.gloc,
+        self.size,
+        .initMany(&.{ .MapRead, .CopyDst }),
+    );
+    defer staging.deinit();
+
+    const enc = c.wgpuDeviceCreateCommandEncoder(self.gloc.device.device, null) orelse return error.Encoder;
+    c.wgpuCommandEncoderCopyBufferToBuffer(enc, self.raw, 0, staging.raw, 0, self.size);
+    const cmd = c.wgpuCommandEncoderFinish(enc, null);
+    defer c.wgpuCommandEncoderRelease(enc);
+    defer c.wgpuCommandBufferRelease(cmd);
+    c.wgpuQueueSubmit(self.gloc.device.queue, 1, &cmd);
+
+    var mapped = false;
+    staging.mapAsync(
+        c.WGPUMapMode_Read,
+        0,
+        self.size,
+        .{ .callback = onMapped, .userdata1 = &mapped },
+    );
+    while (!mapped) self.gloc.device.poll();
+
+    const ptr: [*]const T = @ptrCast(@alignCast(
+        staging.getConstMappedRange(0, self.size),
+    ));
+    @memcpy(out[0..out.len], ptr[0..out.len]);
+    staging.unmap();
+
+    return out;
+}
+
+fn onMapped(
+    status: c.WGPUMapAsyncStatus,
+    _: c.WGPUStringView,
+    userdata1: ?*anyopaque,
+    _: ?*anyopaque,
+) callconv(.c) void {
+    const flag: *bool = @ptrCast(@alignCast(userdata1.?));
+    flag.* = (status == c.WGPUMapAsyncStatus_Success);
+}