1 files changed, 94 insertions, 0 deletions
diff --git a/src/mbgl/geometry/dem_data.cpp b/src/mbgl/geometry/dem_data.cpp
new file mode 100644
index 0000000000..78134dadc1
--- /dev/null
+++ b/src/mbgl/geometry/dem_data.cpp
@@ -0,0 +1,94 @@
+#include <mbgl/geometry/dem_data.hpp>
+#include <mbgl/math/clamp.hpp>
+
+namespace mbgl {
+
+DEMData::DEMData(const PremultipliedImage& _image):
+    dim(_image.size.height),
+    border(std::max<int32_t>(std::ceil(_image.size.height / 2), 1)),
+    stride(dim + 2 * border),
+    image({ static_cast<uint32_t>(stride), static_cast<uint32_t>(stride) }) {
+
+    if (_image.size.height != _image.size.width){
+        throw std::runtime_error("raster-dem tiles must be square.");
+    }
+
+    std::memset(image.data.get(), 0, image.bytes());
+
+    for (int32_t y = 0; y < dim; y++) {
+        for (int32_t x = 0; x < dim; x++) {
+            const int32_t i = y * dim + x;
+            const int32_t j = i * 4;
+            set(x, y, (_image.data[j] * 256 * 256 + _image.data[j+1] * 256 + _image.data[j+2])/10 - 10000);
+        }
+    }
+    
+    // in order to avoid flashing seams between tiles, here we are initially populating a 1px border of
+    // pixels around the image with the data of the nearest pixel from the image. this data is eventually
+    // replaced when the tile's neighboring tiles are loaded and the accurate data can be backfilled using
+    // DEMData#backfillBorder
+
+    for (int32_t x = 0; x < dim; x++) {
+        // left vertical border
+        set(-1, x, get(0, x));
+
+        // right vertical border
+        set(dim, x, get(dim - 1, x));
+
+        //left horizontal border
+        set(x, -1, get(x, 0));
+
+        // right horizontal border
+        set(x, dim, get(x, dim - 1));
+    }
+
+    // corners
+    set(-1, -1, get(0, 0));
+    set(dim, -1, get(dim - 1, 0));
+    set( -1, dim, get(0, dim - 1));
+    set(dim, dim, get(dim - 1, dim - 1));
+}
+
+// This function takes the DEMData from a neighboring tile and backfills the edge/corner
+// data in order to create a one pixel "buffer" of image data around the tile. This is
+// necessary because the hillshade formula calculates the dx/dz, dy/dz derivatives at each
+// pixel of the tile by querying the 8 surrounding pixels, and if we don't have the pixel
+// buffer we get seams at tile boundaries.
+void DEMData::backfillBorder(const DEMData& borderTileData, int8_t dx, int8_t dy) {
+    auto& o = borderTileData;
+
+    // Tiles from the same source should always be of the same dimensions.
+    assert(dim == o.dim);
+
+    // We determine the pixel range to backfill based which corner/edge `borderTileData`
+    // represents. For example, dx = -1, dy = -1 represents the upper left corner of the
+    // base tile, so we only need to backfill one pixel at coordinates (-1, -1) of the tile
+    // image.
+    int32_t _xMin = dx * dim;
+    int32_t _xMax = dx * dim + dim;
+    int32_t _yMin = dy * dim;
+    int32_t _yMax = dy * dim + dim;
+    
+    if (dx == -1) _xMin = _xMax - 1;
+    else if (dx == 1) _xMax = _xMin + 1;
+    
+    if (dy == -1) _yMin = _yMax - 1;
+    else if (dy == 1) _yMax = _yMin + 1;
+    
+    int32_t xMin = util::clamp(_xMin, -border, dim + border);
+    int32_t xMax = util::clamp(_xMax, -border, dim + border);
+    
+    int32_t yMin = util::clamp(_yMin, -border, dim + border);
+    int32_t yMax = util::clamp(_yMax, -border, dim + border);
+    
+    int32_t ox = -dx * dim;
+    int32_t oy = -dy * dim;
+    
+    for (int32_t y = yMin; y < yMax; y++) {
+        for (int32_t x = xMin; x < xMax; x++) {
+            set(x, y, o.get(x + ox, y + oy));
+        }
+    }
+}
+
+} // namespace mbgl