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

include/plot/render/program.hpp

@@ -0,0 +1,62 @@
+#pragma once
+#include <plot/core/color.hpp>
+#include <plot/core/status.hpp>
+#include <plot/gl/handle.hpp>
+#include <plot/math/vec2.hpp>
+
+namespace plot::render {
+
+/// Linked line program and its uniform surface.
+///
+/// It owns the `plot::gl::Program` and knows the GLSL pair (shaders.hpp), so no
+/// caller spells out a uniform name that could drift from the shader. Creating
+/// it propagates what the GL layer reports: `ErrorCode::Unsupported` while
+/// `plot::gl::available()` is false, `GLFailure` plus the driver's log when the
+/// GLSL does not compile or link.
+class LineProgram {
+ public:
+  bool create(Status* st = nullptr) noexcept;
+  bool valid() const noexcept { return program_.id() != 0; }
+  void bind() const noexcept { program_.use(); }
+
+  /// `u_scale`: data space to pixels.
+  void set_scale(Vec2 data_to_px) const noexcept;
+  /// `u_offset`: pixel offset added after `set_scale`.
+  void set_offset(Vec2 px) const noexcept;
+  /// `u_viewport`: render target size in pixels.
+  void set_viewport(Vec2 px) const noexcept;
+  /// `u_width`: stroke width in pixels.
+  void set_width(f32 px) const noexcept;
+  /// `u_color`: stroke colour, alpha included.
+  void set_color(Color color) const noexcept;
+
+ private:
+  gl::Program program_;
+};
+
+/// Linked text program and its uniform surface. It fails exactly the way
+/// `LineProgram::create()` does, propagating `Unsupported` and `GLFailure`.
+///
+/// `create()` also points the `u_atlas` sampler at texture unit 0, which is the
+/// unit `plot::gl::Texture::bind()` defaults to, and leaves this program bound.
+/// The atlas itself stays with the caller, who owns its lifetime.
+class TextProgram {
+ public:
+  bool create(Status* st = nullptr) noexcept;
+  bool valid() const noexcept { return program_.id() != 0; }
+  void bind() const noexcept { program_.use(); }
+
+  /// `u_viewport`: render target size in pixels.
+  void set_viewport(Vec2 px) const noexcept;
+  /// `u_px_range`: pixels per glyph cell, i.e. the on-screen size of one glyph.
+  void set_px_range(Vec2 px) const noexcept;
+  /// `u_tex_size`: atlas size in texels.
+  void set_texture_size(Vec2 texels) const noexcept;
+  /// `u_color`: tint colour, alpha included.
+  void set_color(Color color) const noexcept;
+
+ private:
+  gl::Program program_;
+};
+
+}  // namespace plot::render