feat(render): Renderer with LOD selection, 3.3 and 4.3+ upload paths, headless smoke test

src/render/vertex_array.cpp

@@ -14,11 +14,11 @@ constexpr gl::GLuint kPerInstance = 1;
 
 }  // namespace
 
-bool LineVertexArray::create(Status* st) noexcept {
+bool LineVertexArray::create(Status* st, UploadMode mode) noexcept {
   if (!vao_.create(st)) {
     return false;
   }
-  if (!buffer_.create(st)) {
+  if (!buffer_.create(st, mode)) {
     vao_.reset();  // do not leave a vertex array behind on the failure path
     return false;
   }
@@ -32,6 +32,7 @@ bool LineVertexArray::create(Status* st) noexcept {
   gl::glVertexAttribDivisor(0u, kPerInstance);
   gl::glVertexAttribDivisor(1u, kPerInstance);
   gl::glBindVertexArray(0);  // leave the binding as we found it
+  epoch_ = buffer_.epoch();
   return true;
 }
 
@@ -43,14 +44,26 @@ void LineVertexArray::upload(const f32* interleaved, u32 segments) noexcept {
     return;
   }
   buffer_.upload(interleaved, segments);
+  // Only the mapped transfer moves the instances between slots, and the
+  // attribute offsets have to follow them. The generation changes for a new slot
+  // or a re-created buffer, never otherwise, so the baseline path re-points at
+  // most once.
+  if (buffer_.epoch() != epoch_) {
+    const usize base = buffer_.slot_offset();
+    vao_.bind();
+    buffer_.bind();
+    vao_.attrib(0u, 2, sizeof(LineInstance), base + offsetof(LineInstance, x0));
+    vao_.attrib(1u, 2, sizeof(LineInstance), base + offsetof(LineInstance, x1));
+    epoch_ = buffer_.epoch();
+  }
   instances_ = segments;
 }
 
-bool TextVertexArray::create(Status* st) noexcept {
+bool TextVertexArray::create(Status* st, UploadMode mode) noexcept {
   if (!vao_.create(st)) {
     return false;
   }
-  if (!buffer_.create(st)) {
+  if (!buffer_.create(st, mode)) {
     vao_.reset();
     return false;
   }
@@ -61,6 +74,7 @@ bool TextVertexArray::create(Status* st) noexcept {
   gl::glVertexAttribDivisor(0u, kPerInstance);
   gl::glVertexAttribDivisor(1u, kPerInstance);
   gl::glBindVertexArray(0);
+  epoch_ = buffer_.epoch();
   return true;
 }
 
@@ -70,6 +84,14 @@ void TextVertexArray::upload(const f32* interleaved, u32 glyphs) noexcept {
     return;
   }
   buffer_.upload(interleaved, glyphs);
+  if (buffer_.epoch() != epoch_) {
+    const usize base = buffer_.slot_offset();
+    vao_.bind();
+    buffer_.bind();
+    vao_.attrib(0u, 2, sizeof(TextInstance), base + offsetof(TextInstance, x));
+    vao_.attrib(1u, 2, sizeof(TextInstance), base + offsetof(TextInstance, u));
+    epoch_ = buffer_.epoch();
+  }
   instances_ = glyphs;
 }