Add osc::Texture2D::update_pixel_data to optimize oscimgui backend

Author: adamkewley

liboscar/Graphics/GraphicsImplementation.cpp

@@ -1523,6 +1523,11 @@ class osc::Texture2D::Impl final {
         rgs::copy(pixel_components_row_by_row, pixel_data_.begin());
     }
 
+    void update_pixel_data(const std::function<void(std::span<uint8_t>)>& updater)
+    {
+        updater(pixel_data_);
+    }
+
     // non PIMPL method
 
     gl::Texture2D& updTexture()
@@ -1781,6 +1786,11 @@ void osc::Texture2D::set_pixel_data(std::span<const uint8_t> pixel_components_ro
     impl_.upd()->set_pixel_data(pixel_components_row_by_row);
 }
 
+void osc::Texture2D::update_pixel_data(const std::function<void(std::span<uint8_t>)>& updater)
+{
+    impl_.upd()->update_pixel_data(updater);
+}
+
 std::ostream& osc::operator<<(std::ostream& o, const Texture2D&)
 {
     return o << "Texture2D()";

liboscar/Graphics/Texture2D.h

@@ -10,6 +10,7 @@
 #include <liboscar/Utils/CopyOnUpdSharedValue.h>
 
 #include <cstdint>
+#include <functional>
 #include <iosfwd>
 #include <span>
 #include <vector>
@@ -127,6 +128,10 @@ namespace osc
         std::span<const uint8_t> pixel_data() const;
         void set_pixel_data(std::span<const uint8_t>);
 
+        // Updates this texture's pixel data in-place. Equivalent to calling `pixel_data`, mutating
+        // it, and then passing that to `set_pixel_data`.
+        void update_pixel_data(const std::function<void(std::span<uint8_t>)>& updater);
+
         friend bool operator==(const Texture2D&, const Texture2D&) = default;
 
         class Impl;

liboscar/Graphics/Texture2D.tests.cpp

@@ -200,6 +200,35 @@ TEST(Texture2D, set_pixel_data_on_8bit_component_format_clamps_hdr_color_values)
     ASSERT_NE(texture_2d.pixels(), hdr_pixels);  // because the impl had to convert them
 }
 
+TEST(Texture2D, update_pixel_data_calls_callback_with_span_that_is_identical_to_the_one_returned_from_get_pixel_data)
+{
+    Texture2D texture = generate_2x2_texture();
+    const std::vector<uint8_t> copy(texture.pixel_data().begin(), texture.pixel_data().end());
+    bool called = false;
+    texture.update_pixel_data([&copy, &called](std::span<uint8_t> pixels)
+    {
+        ASSERT_TRUE(rgs::equal(pixels, copy));
+        called = true;
+    });
+    ASSERT_TRUE(called);
+}
+
+TEST(Texture2D, update_pixel_data_makes_subsequent_pixel_data_show_mutated_version)
+{
+    static constexpr uint8_t fill_value = 0x00;
+
+    Texture2D texture = generate_2x2_texture();
+    ASSERT_FALSE(rgs::all_of(texture.pixel_data(), [](uint8_t byte) { return byte == fill_value; }));
+
+    bool called = false;
+    texture.update_pixel_data([&called](std::span<uint8_t> pixels)
+    {
+        rgs::fill(pixels, fill_value);
+        called = true;
+    });
+    ASSERT_TRUE(rgs::all_of(texture.pixel_data(), [](uint8_t byte) { return byte == fill_value; }));
+}
+
 TEST(Texture2D, set_pixels32_on_an_8bit_texture_performs_no_conversion)
 {
     const Color32 color32 = {0x77, 0x63, 0x24, 0x76};

liboscar/UI/oscimgui.cpp

@@ -632,21 +632,21 @@ namespace
             // Fetch the texture handle from the liboscar backend data
             auto* t = bd.lookup_texture(texture_data.GetTexID());
             OSC_ASSERT(t and std::holds_alternative<Texture2D>(*t) && "the texture should've been created by ImTextureStatus_WantCreate");
-            Texture2D& texture = std::get<Texture2D>(*t);
 
             // Update pixel data
-            std::vector<uint8_t> pixel_data_copy(texture.pixel_data().begin(), texture.pixel_data().end());
-            for (const ImTextureRect& source_rect : texture_data.Updates) {
-                uint8_t* source_first_pixel = static_cast<uint8_t*>(texture_data.GetPixelsAt(source_rect.x, source_rect.y));
-                uint8_t* destination_first_pixel = pixel_data_copy.data() + ((source_rect.x + source_rect.y*texture_data.Width) * texture_data.BytesPerPixel);
-                for (int row = 0; row < source_rect.h; ++row) {
-                    uint8_t* source_row_begin = source_first_pixel + (row * texture_data.GetPitch());
-                    uint8_t* source_row_end = source_row_begin + (source_rect.w * texture_data.BytesPerPixel);
-                    uint8_t* destination_row_begin = destination_first_pixel + (row * texture_data.GetPitch());
-                    std::copy(source_row_begin, source_row_end, destination_row_begin);
+            std::get<Texture2D>(*t).update_pixel_data([&texture_data](std::span<uint8_t> pixel_data)
+            {
+                for (const ImTextureRect& source_rect : texture_data.Updates) {
+                    uint8_t* source_first_pixel = static_cast<uint8_t*>(texture_data.GetPixelsAt(source_rect.x, source_rect.y));
+                    uint8_t* destination_first_pixel = pixel_data.data() + ((source_rect.x + source_rect.y*texture_data.Width) * texture_data.BytesPerPixel);
+                    for (int row = 0; row < source_rect.h; ++row) {
+                        uint8_t* source_row_begin = source_first_pixel + (row * texture_data.GetPitch());
+                        uint8_t* source_row_end = source_row_begin + (source_rect.w * texture_data.BytesPerPixel);
+                        uint8_t* destination_row_begin = destination_first_pixel + (row * texture_data.GetPitch());
+                        std::copy(source_row_begin, source_row_end, destination_row_begin);
+                    }
                 }
-            }
-            texture.set_pixel_data(pixel_data_copy);
+            });
             texture_data.SetStatus(ImTextureStatus_OK);
         }
         else if (texture_data.Status == ImTextureStatus_WantDestroy) {