Decode PPI face payloads

src/assets/image_pixels.cpp

@@ -0,0 +1,94 @@
+#include "assets/image_pixels.h"
+
+#include "assets/image_metadata.h"
+
+#include <limits>
+#include <utility>
+
+#define STB_IMAGE_STATIC
+#define STB_IMAGE_IMPLEMENTATION
+#include <stb/stb_image.h>
+
+namespace pp::assets {
+
+namespace {
+
+[[nodiscard]] pp::foundation::Result<std::size_t> rgba_byte_size(
+    std::uint32_t width,
+    std::uint32_t height) noexcept
+{
+    const auto pixels = static_cast<std::uint64_t>(width) * static_cast<std::uint64_t>(height);
+    constexpr auto channels = 4ULL;
+    if (pixels > std::numeric_limits<std::uint64_t>::max() / channels) {
+        return pp::foundation::Result<std::size_t>::failure(
+            pp::foundation::Status::out_of_range("RGBA byte size overflows"));
+    }
+
+    const auto bytes = pixels * channels;
+    if (bytes > static_cast<std::uint64_t>(std::numeric_limits<std::size_t>::max())) {
+        return pp::foundation::Result<std::size_t>::failure(
+            pp::foundation::Status::out_of_range("RGBA byte size exceeds addressable memory"));
+    }
+
+    return pp::foundation::Result<std::size_t>::success(static_cast<std::size_t>(bytes));
+}
+
+}
+
+pp::foundation::Result<Rgba8Image> decode_png_rgba8(std::span<const std::byte> bytes)
+{
+    const auto metadata = parse_png_metadata(bytes);
+    if (!metadata) {
+        return pp::foundation::Result<Rgba8Image>::failure(metadata.status());
+    }
+
+    if (bytes.size() > static_cast<std::size_t>(std::numeric_limits<int>::max())) {
+        return pp::foundation::Result<Rgba8Image>::failure(
+            pp::foundation::Status::out_of_range("PNG payload is too large for the decoder"));
+    }
+
+    int width = 0;
+    int height = 0;
+    int source_components = 0;
+    auto* decoded = stbi_load_from_memory(
+        reinterpret_cast<const stbi_uc*>(bytes.data()),
+        static_cast<int>(bytes.size()),
+        &width,
+        &height,
+        &source_components,
+        4);
+    if (decoded == nullptr) {
+        return pp::foundation::Result<Rgba8Image>::failure(
+            pp::foundation::Status::invalid_argument("PNG payload could not be decoded"));
+    }
+
+    const auto cleanup = [decoded]() noexcept {
+        stbi_image_free(decoded);
+    };
+
+    if (width <= 0 || height <= 0
+        || static_cast<std::uint32_t>(width) != metadata.value().width
+        || static_cast<std::uint32_t>(height) != metadata.value().height) {
+        cleanup();
+        return pp::foundation::Result<Rgba8Image>::failure(
+            pp::foundation::Status::invalid_argument("decoded PNG dimensions are inconsistent"));
+    }
+
+    const auto byte_count = rgba_byte_size(metadata.value().width, metadata.value().height);
+    if (!byte_count) {
+        cleanup();
+        return pp::foundation::Result<Rgba8Image>::failure(byte_count.status());
+    }
+
+    Rgba8Image image {
+        .width = metadata.value().width,
+        .height = metadata.value().height,
+        .pixels = {},
+    };
+    image.pixels.assign(decoded, decoded + byte_count.value());
+    cleanup();
+
+    return pp::foundation::Result<Rgba8Image>::success(std::move(image));
+}
+
+}