The grid worked out for each pixel (as in Blender): one square on its plane, every set of lines showing everywhere their lines are far enough apart on the screen (no patch round the middle, no pieces smearing or fading as you move), a pixel or so wide and smooth, the axes in the colour of the world's axis they run along; in every renderer (drawGrid: a sprite marked by its colour's alpha)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

engine/render/renderer.h

@@ -101,6 +101,11 @@ public:
     // A sprite stretched from `from` to `to`, `width` across (`widthTo` at `to`: < 0, the same),
     // each end turned to face the eye as much as it can (rain; lines drawn in pieces meet exactly).
     void drawStreak(const glm::vec3& from, const glm::vec3& to, float width, const glm::vec4& color, TextureId texture, bool additive = false, float widthTo = -1.0f);
+    // A grid of lines on the plane through `centre` along u and v (unit), drawn for each pixel:
+    // four sets `first` × 10 apart, each showing by how far apart its lines are on the screen,
+    // the axes coloured; look: the lines' shade (0 dark, 1 light), how faint, how strong; fading
+    // out `reach` from the centre.
+    void drawGrid(const glm::vec3& centre, const glm::vec3& u, const glm::vec3& v, float first, const glm::vec3& look, float reach);
     // skin: one matrix per joint (anim::skinMatrices) for skinned models; ignored otherwise.
     // lighting: probe light for moving things (nullptr = lightmap or simple sun shading).
     void drawModel(ModelId model, const glm::mat4& transform, const glm::vec4& tint = glm::vec4(1.0f),