[core] move framebuffer reading to gl::Context

3 files changed, 40 insertions, 0 deletions

diff --git a/src/mbgl/gl/context.cpp b/src/mbgl/gl/context.cpp
index 1cd546f407..811a038caf 100644
--- a/src/mbgl/gl/context.cpp
+++ b/src/mbgl/gl/context.cpp
@@ -92,6 +92,32 @@ UniqueRenderbuffer Context::createRenderbuffer(const RenderbufferType type, cons
     return renderbuffer;
 }
 
+std::unique_ptr<uint8_t[]> Context::readFramebuffer(const Size size, const TextureFormat format, const bool flip) {
+    const size_t stride = size.width * (format == TextureFormat::RGBA ? 4 : 1);
+    auto data = std::make_unique<uint8_t[]>(stride * size.height);
+
+#if not MBGL_USE_GLES2
+    // When reading data from the framebuffer, make sure that we are storing the values
+    // tightly packed into the buffer to avoid buffer overruns.
+    pixelStorePack = { 1 };
+#endif // MBGL_USE_GLES2
+
+    MBGL_CHECK_ERROR(glReadPixels(0, 0, size.width, size.height, static_cast<GLenum>(format),
+                                  GL_UNSIGNED_BYTE, data.get()));
+
+    if (flip) {
+        auto tmp = std::make_unique<uint8_t[]>(stride);
+        uint8_t* rgba = data.get();
+        for (int i = 0, j = size.height - 1; i < j; i++, j--) {
+            std::memcpy(tmp.get(), rgba + i * stride, stride);
+            std::memcpy(rgba + i * stride, rgba + j * stride, stride);
+            std::memcpy(rgba + j * stride, tmp.get(), stride);
+        }
+    }
+
+    return data;
+}
+
 namespace {
 
 void checkFramebuffer() {
diff --git a/src/mbgl/gl/context.hpp b/src/mbgl/gl/context.hpp
index 9bfa54fa55..169aa5566e 100644
--- a/src/mbgl/gl/context.hpp
+++ b/src/mbgl/gl/context.hpp
@@ -62,6 +62,15 @@ public:
                                   const Renderbuffer<RenderbufferType::DepthStencil>&);
     Framebuffer createFramebuffer(const Texture&);
 
+    template <typename Image,
+              TextureFormat format = Image::channels == 4 ? TextureFormat::RGBA
+                                                          : TextureFormat::Alpha>
+    Image readFramebuffer(const Size size, bool flip = true) {
+        static_assert(Image::channels == (format == TextureFormat::RGBA ? 4 : 1),
+                      "image format mismatch");
+        return { size, readFramebuffer(size, format, flip) };
+    }
+
     // Create a texture from an image with data.
     template <typename Image>
     Texture createTexture(const Image& image, TextureUnit unit = 0) {
@@ -167,6 +176,7 @@ private:
     void updateTexture(TextureID, Size size, const void* data, TextureFormat, TextureUnit);
     UniqueFramebuffer createFramebuffer();
     UniqueRenderbuffer createRenderbuffer(RenderbufferType, Size size);
+    std::unique_ptr<uint8_t[]> readFramebuffer(Size, TextureFormat, bool flip);
 
     PrimitiveType operator()(const Points&);
     PrimitiveType operator()(const Lines&);
diff --git a/src/mbgl/gl/types.hpp b/src/mbgl/gl/types.hpp
index 6e1bc5f8e1..1697656469 100644
--- a/src/mbgl/gl/types.hpp
+++ b/src/mbgl/gl/types.hpp
@@ -50,6 +50,10 @@ enum class TextureWrap : bool { Clamp, Repeat };
 enum class TextureFormat : uint32_t {
     RGBA = 0x1908,
     Alpha = 0x1906,
+#if not MBGL_USE_GLES2
+    Stencil = 0x1901,
+    Depth = 0x1902,
+#endif // MBGL_USE_GLES2
 };
 
 enum class PrimitiveType {