Add image export roundtrip automation

src/assets/image_pixels.cpp

@@ -9,6 +9,10 @@
 #define STB_IMAGE_IMPLEMENTATION
 #include <stb/stb_image.h>
 
+#define STB_IMAGE_WRITE_STATIC
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#include <stb/stb_image_write.h>
+
 namespace pp::assets {
 
 namespace {
@@ -33,6 +37,17 @@ namespace {
     return pp::foundation::Result<std::size_t>::success(static_cast<std::size_t>(bytes));
 }
 
+void append_png_bytes(void* context, void* data, int size)
+{
+    if (context == nullptr || data == nullptr || size <= 0) {
+        return;
+    }
+
+    auto* bytes = static_cast<std::vector<std::byte>*>(context);
+    const auto* begin = static_cast<const std::byte*>(data);
+    bytes->insert(bytes->end(), begin, begin + size);
+}
+
 }
 
 pp::foundation::Result<Rgba8Image> decode_png_rgba8(std::span<const std::byte> bytes)
@@ -91,4 +106,54 @@ pp::foundation::Result<Rgba8Image> decode_png_rgba8(std::span<const std::byte> b
     return pp::foundation::Result<Rgba8Image>::success(std::move(image));
 }
 
+pp::foundation::Result<std::vector<std::byte>> encode_png_rgba8(
+    std::uint32_t width,
+    std::uint32_t height,
+    std::span<const std::uint8_t> pixels)
+{
+    if (width == 0 || height == 0) {
+        return pp::foundation::Result<std::vector<std::byte>>::failure(
+            pp::foundation::Status::invalid_argument("PNG dimensions must be greater than zero"));
+    }
+
+    if (width > static_cast<std::uint32_t>(std::numeric_limits<int>::max())
+        || height > static_cast<std::uint32_t>(std::numeric_limits<int>::max())) {
+        return pp::foundation::Result<std::vector<std::byte>>::failure(
+            pp::foundation::Status::out_of_range("PNG dimensions exceed encoder limits"));
+    }
+
+    const auto byte_count = rgba_byte_size(width, height);
+    if (!byte_count) {
+        return pp::foundation::Result<std::vector<std::byte>>::failure(byte_count.status());
+    }
+
+    if (pixels.size() != byte_count.value()) {
+        return pp::foundation::Result<std::vector<std::byte>>::failure(
+            pp::foundation::Status::invalid_argument("RGBA pixel payload size does not match dimensions"));
+    }
+
+    const auto stride = static_cast<std::uint64_t>(width) * 4ULL;
+    if (stride > static_cast<std::uint64_t>(std::numeric_limits<int>::max())) {
+        return pp::foundation::Result<std::vector<std::byte>>::failure(
+            pp::foundation::Status::out_of_range("PNG row stride exceeds encoder limits"));
+    }
+
+    std::vector<std::byte> encoded;
+    const auto result = stbi_write_png_to_func(
+        append_png_bytes,
+        &encoded,
+        static_cast<int>(width),
+        static_cast<int>(height),
+        4,
+        pixels.data(),
+        static_cast<int>(stride));
+
+    if (result == 0 || encoded.empty()) {
+        return pp::foundation::Result<std::vector<std::byte>>::failure(
+            pp::foundation::Status::invalid_argument("RGBA pixels could not be encoded as PNG"));
+    }
+
+    return pp::foundation::Result<std::vector<std::byte>>::success(std::move(encoded));
+}
+
 }

src/assets/image_pixels.h

@@ -18,4 +18,9 @@ struct Rgba8Image {
 [[nodiscard]] pp::foundation::Result<Rgba8Image> decode_png_rgba8(
     std::span<const std::byte> bytes);
 
+[[nodiscard]] pp::foundation::Result<std::vector<std::byte>> encode_png_rgba8(
+    std::uint32_t width,
+    std::uint32_t height,
+    std::span<const std::uint8_t> pixels);
+
 }