Preserve 16:9 tile aspect on resize

TileLayout.cpp

@@ -21,46 +21,116 @@ std::vector<Vertex> makeQuad(
         {{x0, y1}, {0.0f, 1.0f}},
     };
 }
+
+float toNdcX(float x, float viewportWidth)
+{
+    return x * 2.0f / viewportWidth - 1.0f;
 }
 
-std::vector<Vertex> makeGridLayout(
+float toNdcY(float y, float viewportHeight)
+{
+    return y * 2.0f / viewportHeight - 1.0f;
+}
+}
+
+std::vector<TileRect> makeGridTileRects(
     uint32_t cols,
     uint32_t rows,
-    float gapX,
-    float gapY)
+    float viewportWidth,
+    float viewportHeight,
+    float gapPixels,
+    float targetAspect)
 {
-    std::vector<Vertex> vertices;
-    vertices.reserve(
-        static_cast<size_t>(cols) * rows * 6);
+    std::vector<TileRect> rects;
+    rects.reserve(static_cast<size_t>(cols) * rows);
 
-    const float tileW =
-        (2.0f - gapX * static_cast<float>(cols - 1)) /
+    if (cols == 0 || rows == 0 ||
+        viewportWidth <= 0.0f || viewportHeight <= 0.0f ||
+        targetAspect <= 0.0f)
+    {
+        return rects;
+    }
+
+    const float gapX =
+        std::min(gapPixels, viewportWidth * 0.1f);
+    const float gapY =
+        std::min(gapPixels, viewportHeight * 0.1f);
+
+    const float cellW =
+        (viewportWidth - gapX * static_cast<float>(cols - 1)) /
         static_cast<float>(cols);
-    const float tileH =
-        (2.0f - gapY * static_cast<float>(rows - 1)) /
+    const float cellH =
+        (viewportHeight - gapY * static_cast<float>(rows - 1)) /
         static_cast<float>(rows);
 
+    float tileW = cellW;
+    float tileH = tileW / targetAspect;
+
+    if (tileH > cellH)
+    {
+        tileH = cellH;
+        tileW = tileH * targetAspect;
+    }
+
+    const float insetX = (cellW - tileW) * 0.5f;
+    const float insetY = (cellH - tileH) * 0.5f;
+
     for (uint32_t row = 0; row < rows; ++row)
     {
         for (uint32_t col = 0; col < cols; ++col)
         {
             const float x0 =
-                -1.0f +
-                static_cast<float>(col) * (tileW + gapX);
+                static_cast<float>(col) * (cellW + gapX) +
+                insetX;
             const float y0 =
-                -1.0f +
-                static_cast<float>(row) * (tileH + gapY);
+                static_cast<float>(row) * (cellH + gapY) +
+                insetY;
             const float x1 = x0 + tileW;
             const float y1 = y0 + tileH;
 
-            auto quad = makeQuad(x0, y0, x1, y1);
-            vertices.insert(
-                vertices.end(),
-                quad.begin(),
-                quad.end());
+            rects.push_back({x0, y0, x1, y1});
         }
     }
 
+    return rects;
+}
+
+std::vector<Vertex> makeGridLayout(
+    uint32_t cols,
+    uint32_t rows,
+    float viewportWidth,
+    float viewportHeight,
+    float gapPixels,
+    float targetAspect)
+{
+    std::vector<Vertex> vertices;
+    vertices.reserve(
+        static_cast<size_t>(cols) * rows * 6);
+
+    std::vector<TileRect> rects =
+        makeGridTileRects(
+            cols,
+            rows,
+            viewportWidth,
+            viewportHeight,
+            gapPixels,
+            targetAspect
+        );
+
+    for (const TileRect& rect : rects)
+    {
+        auto quad = makeQuad(
+            toNdcX(rect.x0, viewportWidth),
+            toNdcY(rect.y0, viewportHeight),
+            toNdcX(rect.x1, viewportWidth),
+            toNdcY(rect.y1, viewportHeight)
+        );
+        vertices.insert(
+            vertices.end(),
+            quad.begin(),
+            quad.end());
+    }
+
     return vertices;
 }
 
@@ -68,11 +138,20 @@ void updateGridLayout(
     Vertex* vertices,
     uint32_t cols,
     uint32_t rows,
-    float gapX,
-    float gapY)
+    float viewportWidth,
+    float viewportHeight,
+    float gapPixels,
+    float targetAspect)
 {
     std::vector<Vertex> updated =
-        makeGridLayout(cols, rows, gapX, gapY);
+        makeGridLayout(
+            cols,
+            rows,
+            viewportWidth,
+            viewportHeight,
+            gapPixels,
+            targetAspect
+        );
 
     std::copy(
         updated.begin(),