scratch_buffer: Explicitly defing resize and resize_destructive functions

resize keeps previous data intact when the buffer grows
resize_destructive destroys the previous data when the buffer grows

src/common/scratch_buffer.h

@@ -25,7 +25,20 @@ public:
     ~ScratchBuffer() = default;
 
     /// This will only grow the buffer's capacity if size is greater than the current capacity.
+    /// The previously held data will remain intact.
     void resize(size_t size) {
+        if (size > buffer_capacity) {
+            auto new_buffer = Common::make_unique_for_overwrite<T[]>(size);
+            std::move(buffer.get(), buffer.get() + buffer_capacity, new_buffer.get());
+            buffer = std::move(new_buffer);
+            buffer_capacity = size;
+        }
+        last_requested_size = size;
+    }
+
+    /// This will only grow the buffer's capacity if size is greater than the current capacity.
+    /// The previously held data will be destroyed if a reallocation occurs.
+    void resize_destructive(size_t size) {
         if (size > buffer_capacity) {
             buffer_capacity = size;
             buffer = Common::make_unique_for_overwrite<T[]>(buffer_capacity);
@@ -61,6 +74,10 @@ public:
         return buffer[i];
     }
 
+    [[nodiscard]] const T& operator[](size_t i) const {
+        return buffer[i];
+    }
+
     [[nodiscard]] size_t size() const noexcept {
         return last_requested_size;
     }

src/tests/common/scratch_buffer.cpp

@@ -29,7 +29,7 @@ TEST_CASE("ScratchBuffer: Basic Test", "[common]") {
     }
 }
 
-TEST_CASE("ScratchBuffer: Resize Grow", "[common]") {
+TEST_CASE("ScratchBuffer: resize_destructive Grow", "[common]") {
     std::array<u8, 10> payload;
     payload.fill(66);
 
@@ -38,14 +38,86 @@ TEST_CASE("ScratchBuffer: Resize Grow", "[common]") {
     REQUIRE(buf.capacity() == payload.size());
 
     // Increasing the size should reallocate the buffer
-    buf.resize(payload.size() * 2);
+    buf.resize_destructive(payload.size() * 2);
     REQUIRE(buf.size() == payload.size() * 2);
     REQUIRE(buf.capacity() == payload.size() * 2);
 
     // Since the buffer is not value initialized, reading its data will be garbage
 }
 
-TEST_CASE("ScratchBuffer: Resize Shrink", "[common]") {
+TEST_CASE("ScratchBuffer: resize_destructive Shrink", "[common]") {
+    std::array<u8, 10> payload;
+    payload.fill(66);
+
+    ScratchBuffer<u8> buf(payload.size());
+    REQUIRE(buf.size() == payload.size());
+    REQUIRE(buf.capacity() == payload.size());
+
+    std::memcpy(buf.data(), payload.data(), payload.size());
+    for (size_t i = 0; i < payload.size(); ++i) {
+        REQUIRE(buf[i] == payload[i]);
+    }
+
+    // Decreasing the size should not cause a buffer reallocation
+    // This can be tested by ensuring the buffer capacity and data has not changed,
+    buf.resize_destructive(1U);
+    REQUIRE(buf.size() == 1U);
+    REQUIRE(buf.capacity() == payload.size());
+
+    for (size_t i = 0; i < payload.size(); ++i) {
+        REQUIRE(buf[i] == payload[i]);
+    }
+}
+
+TEST_CASE("ScratchBuffer: resize Grow u8", "[common]") {
+    std::array<u8, 10> payload;
+    payload.fill(66);
+
+    ScratchBuffer<u8> buf(payload.size());
+    REQUIRE(buf.size() == payload.size());
+    REQUIRE(buf.capacity() == payload.size());
+
+    std::memcpy(buf.data(), payload.data(), payload.size());
+    for (size_t i = 0; i < payload.size(); ++i) {
+        REQUIRE(buf[i] == payload[i]);
+    }
+
+    // Increasing the size should reallocate the buffer
+    buf.resize(payload.size() * 2);
+    REQUIRE(buf.size() == payload.size() * 2);
+    REQUIRE(buf.capacity() == payload.size() * 2);
+
+    // resize() keeps the previous data intact
+    for (size_t i = 0; i < payload.size(); ++i) {
+        REQUIRE(buf[i] == payload[i]);
+    }
+}
+
+TEST_CASE("ScratchBuffer: resize Grow u64", "[common]") {
+    std::array<u64, 10> payload;
+    payload.fill(6666);
+
+    ScratchBuffer<u64> buf(payload.size());
+    REQUIRE(buf.size() == payload.size());
+    REQUIRE(buf.capacity() == payload.size());
+
+    std::memcpy(buf.data(), payload.data(), payload.size() * sizeof(u64));
+    for (size_t i = 0; i < payload.size(); ++i) {
+        REQUIRE(buf[i] == payload[i]);
+    }
+
+    // Increasing the size should reallocate the buffer
+    buf.resize(payload.size() * 2);
+    REQUIRE(buf.size() == payload.size() * 2);
+    REQUIRE(buf.capacity() == payload.size() * 2);
+
+    // resize() keeps the previous data intact
+    for (size_t i = 0; i < payload.size(); ++i) {
+        REQUIRE(buf[i] == payload[i]);
+    }
+}
+
+TEST_CASE("ScratchBuffer: resize Shrink", "[common]") {
     std::array<u8, 10> payload;
     payload.fill(66);
 

src/video_core/buffer_cache/buffer_cache.h

@@ -1926,7 +1926,7 @@ std::span<const u8> BufferCache<P>::ImmediateBufferWithData(VAddr cpu_addr, size
 
 template <class P>
 std::span<u8> BufferCache<P>::ImmediateBuffer(size_t wanted_capacity) {
-    immediate_buffer_alloc.resize(wanted_capacity);
+    immediate_buffer_alloc.resize_destructive(wanted_capacity);
     return std::span<u8>(immediate_buffer_alloc.data(), wanted_capacity);
 }
 

src/video_core/dma_pusher.cpp

@@ -74,7 +74,7 @@ bool DmaPusher::Step() {
         }
 
         // Push buffer non-empty, read a word
-        command_headers.resize(command_list_header.size);
+        command_headers.resize_destructive(command_list_header.size);
         if (Settings::IsGPULevelHigh()) {
             memory_manager.ReadBlock(dma_get, command_headers.data(),
                                      command_list_header.size * sizeof(u32));

src/video_core/engines/engine_upload.cpp

@@ -24,7 +24,7 @@ void State::BindRasterizer(VideoCore::RasterizerInterface* rasterizer_) {
 void State::ProcessExec(const bool is_linear_) {
     write_offset = 0;
     copy_size = regs.line_length_in * regs.line_count;
-    inner_buffer.resize(copy_size);
+    inner_buffer.resize_destructive(copy_size);
     is_linear = is_linear_;
 }
 
@@ -70,7 +70,7 @@ void State::ProcessData(std::span<const u8> read_buffer) {
         const std::size_t dst_size = Tegra::Texture::CalculateSize(
             true, bytes_per_pixel, width, regs.dest.height, regs.dest.depth,
             regs.dest.BlockHeight(), regs.dest.BlockDepth());
-        tmp_buffer.resize(dst_size);
+        tmp_buffer.resize_destructive(dst_size);
         memory_manager.ReadBlock(address, tmp_buffer.data(), dst_size);
         Tegra::Texture::SwizzleSubrect(tmp_buffer, read_buffer, bytes_per_pixel, width,
                                        regs.dest.height, regs.dest.depth, x_offset, regs.dest.y,

src/video_core/engines/maxwell_dma.cpp

@@ -184,8 +184,8 @@ void MaxwellDMA::CopyBlockLinearToPitch() {
     const size_t src_size =
         CalculateSize(true, bytes_per_pixel, width, height, depth, block_height, block_depth);
 
-    read_buffer.resize(src_size);
-    write_buffer.resize(dst_size);
+    read_buffer.resize_destructive(src_size);
+    write_buffer.resize_destructive(dst_size);
 
     memory_manager.ReadBlock(regs.offset_in, read_buffer.data(), src_size);
     memory_manager.ReadBlock(regs.offset_out, write_buffer.data(), dst_size);
@@ -231,8 +231,8 @@ void MaxwellDMA::CopyPitchToBlockLinear() {
         CalculateSize(true, bytes_per_pixel, width, height, depth, block_height, block_depth);
     const size_t src_size = static_cast<size_t>(regs.pitch_in) * regs.line_count;
 
-    read_buffer.resize(src_size);
-    write_buffer.resize(dst_size);
+    read_buffer.resize_destructive(src_size);
+    write_buffer.resize_destructive(dst_size);
 
     memory_manager.ReadBlock(regs.offset_in, read_buffer.data(), src_size);
     if (Settings::IsGPULevelExtreme()) {
@@ -261,8 +261,8 @@ void MaxwellDMA::FastCopyBlockLinearToPitch() {
     pos_x = pos_x % x_in_gob;
     pos_y = pos_y % 8;
 
-    read_buffer.resize(src_size);
-    write_buffer.resize(dst_size);
+    read_buffer.resize_destructive(src_size);
+    write_buffer.resize_destructive(dst_size);
 
     if (Settings::IsGPULevelExtreme()) {
         memory_manager.ReadBlock(regs.offset_in + offset, read_buffer.data(), src_size);
@@ -321,10 +321,10 @@ void MaxwellDMA::CopyBlockLinearToBlockLinear() {
     const u32 pitch = x_elements * bytes_per_pixel;
     const size_t mid_buffer_size = pitch * regs.line_count;
 
-    read_buffer.resize(src_size);
-    write_buffer.resize(dst_size);
+    read_buffer.resize_destructive(src_size);
+    write_buffer.resize_destructive(dst_size);
 
-    intermediate_buffer.resize(mid_buffer_size);
+    intermediate_buffer.resize_destructive(mid_buffer_size);
 
     memory_manager.ReadBlock(regs.offset_in, read_buffer.data(), src_size);
     memory_manager.ReadBlock(regs.offset_out, write_buffer.data(), dst_size);

src/video_core/host1x/vic.cpp

@@ -155,7 +155,7 @@ void Vic::WriteRGBFrame(const AVFrame* frame, const VicConfig& config) {
         // swizzle pitch linear to block linear
         const u32 block_height = static_cast<u32>(config.block_linear_height_log2);
         const auto size = Texture::CalculateSize(true, 4, width, height, 1, block_height, 0);
-        luma_buffer.resize(size);
+        luma_buffer.resize_destructive(size);
         std::span<const u8> frame_buff(converted_frame_buf_addr, 4 * width * height);
         Texture::SwizzleSubrect(luma_buffer, frame_buff, 4, width, height, 1, 0, 0, width, height,
                                 block_height, 0, width * 4);
@@ -181,8 +181,8 @@ void Vic::WriteYUVFrame(const AVFrame* frame, const VicConfig& config) {
 
     const auto stride = static_cast<size_t>(frame->linesize[0]);
 
-    luma_buffer.resize(aligned_width * surface_height);
-    chroma_buffer.resize(aligned_width * surface_height / 2);
+    luma_buffer.resize_destructive(aligned_width * surface_height);
+    chroma_buffer.resize_destructive(aligned_width * surface_height / 2);
 
     // Populate luma buffer
     const u8* luma_src = frame->data[0];