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

include/plot/render/vertex_array.hpp

@@ -0,0 +1,54 @@
+#pragma once
+#include <plot/core/status.hpp>
+#include <plot/core/types.hpp>
+#include <plot/gl/handle.hpp>
+#include <plot/render/buffer.hpp>
+
+namespace plot::render {
+
+/// Vertex array plus instance buffer of the line pipeline.
+///
+/// The attribute layout is fixed by the line shader (see shaders.hpp): `a_p0` at
+/// location 0 and `a_p1` at location 1, two floats each, advancing once per
+/// instance. A caller never writes a location, stride or offset; it stages a
+/// `LineBatch` and uploads its `data()`.
+class LineVertexArray {
+ public:
+  /// Creates the vertex array, the instance buffer and the attribute layout.
+  bool create(Status* st = nullptr) noexcept;
+
+  /// Uploads `segments` instances from interleaved `x0,y0,x1,y1` floats and
+  /// records how many the next draw should rasterise.
+  void upload(const f32* interleaved, u32 segments) noexcept;
+
+  void bind() const noexcept { vao_.bind(); }
+  bool valid() const noexcept { return vao_.id() != 0; }
+  u32 instance_count() const noexcept { return instances_; }
+
+ private:
+  LineBuffer buffer_;
+  gl::VertexArray vao_;
+  u32 instances_ = 0;
+};
+
+/// Vertex array plus instance buffer of the text pipeline: `a_pos` at location 0
+/// and the glyph's atlas texel origin `a_uv` at location 1, two floats each,
+/// advancing once per instance.
+class TextVertexArray {
+ public:
+  bool create(Status* st = nullptr) noexcept;
+
+  /// Uploads `glyphs` instances from interleaved `x,y,u,v` floats.
+  void upload(const f32* interleaved, u32 glyphs) noexcept;
+
+  void bind() const noexcept { vao_.bind(); }
+  bool valid() const noexcept { return vao_.id() != 0; }
+  u32 instance_count() const noexcept { return instances_; }
+
+ private:
+  TextBuffer buffer_;
+  gl::VertexArray vao_;
+  u32 instances_ = 0;
+};
+
+}  // namespace plot::render