feat(render): style, GLSL line/text pipelines, staging batches, bitmap font

src/render/primitives.cpp

@@ -0,0 +1,61 @@
+#include <plot/render/primitives.hpp>
+
+namespace plot::render {
+
+// ----------------------------------------------------------------- LineBatch
+
+void LineBatch::begin() noexcept { v_.clear(); }
+
+void LineBatch::clear() noexcept { v_.clear(); }
+
+void LineBatch::add_segment(Vec2 a, Vec2 b) {
+  v_.push_back(a.x);
+  v_.push_back(a.y);
+  v_.push_back(b.x);
+  v_.push_back(b.y);
+}
+
+void LineBatch::add_polyline(const Vec2* pts, u32 n) {
+  if (pts == nullptr || n < 2u) {
+    return;  // no pair of points, no segment
+  }
+  // Grow once for the whole polyline rather than per segment, so a frame that
+  // stages the same workload as the last one never reallocates.
+  v_.reserve(v_.size() + 4u * (n - 1u));
+  for (u32 i = 1; i < n; ++i) {
+    add_segment(pts[i - 1u], pts[i]);
+  }
+}
+
+// ----------------------------------------------------------------- TextBatch
+
+void TextBatch::begin() noexcept { v_.clear(); }
+
+void TextBatch::clear() noexcept { v_.clear(); }
+
+void TextBatch::add_glyph(Vec2 pos_px, u32 slot) {
+  const Vec2 origin = BitmapFont::atlas_origin(slot);
+  v_.push_back(pos_px.x);
+  v_.push_back(pos_px.y);
+  v_.push_back(origin.x);
+  v_.push_back(origin.y);
+}
+
+Vec2 TextBatch::add_text(Vec2 pen_px, const char* utf8, const BitmapFont& font, f32 px_per_cell) {
+  if (utf8 == nullptr) {
+    return pen_px;
+  }
+  const f32 scale = px_per_cell / static_cast<f32>(BitmapFont::kGlyphPx);
+  for (const char* p = utf8; *p != '\0';) {
+    // Same codepoints `measure` sums and the same advances, scaled by the
+    // on-screen cell size: a run staged here is exactly what the plot layer
+    // measured, times the scale it draws at, so a label never overruns the
+    // space that was reserved for it.
+    const u32 codepoint = BitmapFont::next_codepoint(p);
+    add_glyph(pen_px, BitmapFont::glyph_index(codepoint));
+    pen_px.x += font.advance_codepoint(codepoint) * scale;
+  }
+  return pen_px;
+}
+
+}  // namespace plot::render