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

src/render/vertex_array.cpp

@@ -0,0 +1,76 @@
+#include <plot/render/vertex_array.hpp>
+
+#include <plot/gl/api.hpp>
+
+#include <cstddef>
+
+namespace plot::render {
+namespace {
+
+/// Instance data advances one step per instance, never per vertex: both
+/// pipelines draw one quad per instance with corners synthesised from
+/// `gl_VertexID`, so every attribute has a divisor of 1 (core since GL 3.3).
+constexpr gl::GLuint kPerInstance = 1;
+
+}  // namespace
+
+bool LineVertexArray::create(Status* st) noexcept {
+  if (!vao_.create(st)) {
+    return false;
+  }
+  if (!buffer_.create(st)) {
+    vao_.reset();  // do not leave a vertex array behind on the failure path
+    return false;
+  }
+  // Attribute pointers capture the bound GL_ARRAY_BUFFER, so bind both first.
+  vao_.bind();
+  buffer_.bind();
+  // Offsets come from the struct, not from counting floats: the layout is the
+  // one shaders.hpp declares, and it stays in step with LineInstance.
+  vao_.attrib(0u, 2, sizeof(LineInstance), offsetof(LineInstance, x0));
+  vao_.attrib(1u, 2, sizeof(LineInstance), offsetof(LineInstance, x1));
+  gl::glVertexAttribDivisor(0u, kPerInstance);
+  gl::glVertexAttribDivisor(1u, kPerInstance);
+  gl::glBindVertexArray(0);  // leave the binding as we found it
+  return true;
+}
+
+void LineVertexArray::upload(const f32* interleaved, u32 segments) noexcept {
+  // An array that was never created reports nothing to draw, so a caller that
+  // ignored create()'s status rasterises nothing instead of stale memory.
+  if (interleaved == nullptr || vao_.id() == 0) {
+    instances_ = 0;
+    return;
+  }
+  buffer_.upload(interleaved, segments);
+  instances_ = segments;
+}
+
+bool TextVertexArray::create(Status* st) noexcept {
+  if (!vao_.create(st)) {
+    return false;
+  }
+  if (!buffer_.create(st)) {
+    vao_.reset();
+    return false;
+  }
+  vao_.bind();
+  buffer_.bind();
+  vao_.attrib(0u, 2, sizeof(TextInstance), offsetof(TextInstance, x));
+  vao_.attrib(1u, 2, sizeof(TextInstance), offsetof(TextInstance, u));
+  gl::glVertexAttribDivisor(0u, kPerInstance);
+  gl::glVertexAttribDivisor(1u, kPerInstance);
+  gl::glBindVertexArray(0);
+  return true;
+}
+
+void TextVertexArray::upload(const f32* interleaved, u32 glyphs) noexcept {
+  if (interleaved == nullptr || vao_.id() == 0) {
+    instances_ = 0;
+    return;
+  }
+  buffer_.upload(interleaved, glyphs);
+  instances_ = glyphs;
+}
+
+}  // namespace plot::render