4 files changed, 131 insertions, 21 deletions

diff --git a/gfx/include/gfx/renderer.h b/gfx/include/gfx/renderer.h
index 13e6c2c..c420889 100644
--- a/gfx/include/gfx/renderer.h
+++ b/gfx/include/gfx/renderer.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <math/aabb2.h>
 #include <math/aabb3.h>
 #include <math/camera.h>
 #include <math/mat4.h>
@@ -56,13 +57,31 @@ void gfx_imm_draw_triangles(ImmRenderer*, const vec3[], size_t num_triangles);
 void gfx_imm_draw_triangle(ImmRenderer*, const vec3[3]);
 
 /// Draw a bounding box.
-void gfx_imm_draw_aabb(ImmRenderer*, aabb3);
+void gfx_imm_draw_aabb2(ImmRenderer*, aabb2);
+
+/// Draw a bounding box.
+void gfx_imm_draw_aabb3(ImmRenderer*, aabb3);
 
 /// Set the camera.
 void gfx_imm_set_camera(ImmRenderer*, const Camera*);
 
-/// Set the model matrix.
+/// Load an identity model matrix. Clears the matrix stack.
+void gfx_imm_load_identity(ImmRenderer* renderer);
+
+/// Push the given matrix to the matrix stack.
+void gfx_imm_push_matrix(ImmRenderer* renderer, const mat4* matrix);
+
+/// Pop the top of the matrix stack.
+void gfx_imm_pop_matrix(ImmRenderer* renderer);
+
+/// Push a translation matrix to the matrix stack.
+void gfx_imm_translate(ImmRenderer* renderer, vec3 offset);
+
+/// Set the model matrix. Clears the matrix stack.
 void gfx_imm_set_model_matrix(ImmRenderer*, const mat4*);
 
+/// Set the view-projection matrix.
+void gfx_imm_set_view_projection_matrix(ImmRenderer*, const mat4*);
+
 /// Set the render colour.
 void gfx_imm_set_colour(ImmRenderer*, vec4 colour);
diff --git a/gfx/include/gfx/sizes.h b/gfx/include/gfx/sizes.h
index 9f13e30..f2ace8a 100644
--- a/gfx/include/gfx/sizes.h
+++ b/gfx/include/gfx/sizes.h
@@ -80,6 +80,9 @@
 /// frame.
 #define IMM_MAX_NUM_TRIANGLES 1024
 
+/// Maximum number of matrices in the immediate-mode renderer's matrix stack.
+#define IMM_MAX_NUM_MATRICES 32
+
 // Gfx.
 
 #define GFX_MAX_NUM_SCENES 4
diff --git a/gfx/src/renderer/imm_renderer.c b/gfx/src/renderer/imm_renderer.c
index 12b642c..492c7af 100644
--- a/gfx/src/renderer/imm_renderer.c
+++ b/gfx/src/renderer/imm_renderer.c
@@ -33,6 +33,9 @@ bool imm_renderer_make(ImmRenderer* renderer, RenderBackend* render_backend) {
     goto cleanup;
   }
 
+  renderer->matrix_stack[0] = mat4_id();
+  renderer->stack_pointer   = 0;
+
   gfx_imm_set_colour(renderer, vec4_make(0.0, 0.0, 0.0, 1.0));
 
   return true;
@@ -79,17 +82,16 @@ void imm_renderer_flush(ImmRenderer* renderer) {
 void gfx_imm_start(ImmRenderer* renderer) {
   assert(renderer);
 
+  // Shader uniforms are applied lazily.
+  // TODO: In the event that gfx_activate_shader_program() activates uniforms
+  // automatically for convenience, call an overload here that doesn't do so.
   ShaderProgram* shader = renderer->shader;
   gfx_activate_shader_program(shader);
-  // TODO: Having to apply manually is annoying. Maybe just apply implicitly
-  // when the program is activated?
-  // Note that then we'll need to be able to just gfx_apply_uniforms() in
-  // flush().
-  // gfx_set_culling(renderer->render_backend, false);
-  gfx_apply_uniforms(shader);
-  gfx_set_blending(renderer->render_backend, true);
-  gfx_set_depth_mask(renderer->render_backend, false);
-  gfx_set_polygon_offset(renderer->render_backend, 0.5f, 0.5f);
+
+  // TODO: Move this to the gltf_view program.
+  //  gfx_set_blending(renderer->render_backend, true);
+  //  gfx_set_depth_mask(renderer->render_backend, false);
+  //  gfx_set_polygon_offset(renderer->render_backend, 0.5f, 0.5f);
 }
 
 void gfx_imm_end(ImmRenderer* renderer) {
@@ -97,10 +99,11 @@ void gfx_imm_end(ImmRenderer* renderer) {
 
   imm_renderer_flush(renderer);
 
-  gfx_set_polygon_offset(renderer->render_backend, 0.0f, 0.0f);
-  gfx_set_depth_mask(renderer->render_backend, true);
-  gfx_set_blending(renderer->render_backend, false);
-  // gfx_set_culling(renderer->render_backend, true);
+  // TODO: Move this to the gltf_view program.
+  //  gfx_set_polygon_offset(renderer->render_backend, 0.0f, 0.0f);
+  //  gfx_set_depth_mask(renderer->render_backend, true);
+  //  gfx_set_blending(renderer->render_backend, false);
+
   gfx_deactivate_shader_program(renderer->shader);
 }
 
@@ -123,9 +126,28 @@ void gfx_imm_draw_triangle(ImmRenderer* renderer, const vec3 verts[3]) {
   gfx_imm_draw_triangles(renderer, verts, 1);
 }
 
-void gfx_imm_draw_aabb(ImmRenderer* renderer, aabb3 box) {
+void gfx_imm_draw_aabb2(ImmRenderer* renderer, aabb2 box) {
+  assert(renderer);
+
+  // clang-format off
+  const vec3 verts[4] = {
+      vec3_make(box.min.x, box.min.y, 0),    // 3 ---- 2
+      vec3_make(box.max.x, box.min.y, 0),    // |      |
+      vec3_make(box.max.x, box.max.y, 0),    // |      |
+      vec3_make(box.min.x, box.max.y, 0)};   // 0 ---- 1
+  // clang-format on
+
+#define tri(i0, i1, i2) verts[i0], verts[i1], verts[i2]
+  const vec3 tris[6] = {tri(0, 1, 2), tri(0, 2, 3)};
+#undef tri
+
+  gfx_imm_draw_triangles(renderer, tris, 2);
+}
+
+void gfx_imm_draw_aabb3(ImmRenderer* renderer, aabb3 box) {
   assert(renderer);
 
+  // clang-format off
   const vec3 verts[8] = {
       box.min,                                    //     2 ----- 6
       vec3_make(box.min.x, box.min.y, box.max.z), //    /       /|
@@ -135,9 +157,9 @@ void gfx_imm_draw_aabb(ImmRenderer* renderer, aabb3 box) {
       vec3_make(box.max.x, box.min.y, box.max.z), //   |/      |/
       vec3_make(box.max.x, box.max.y, box.min.z), //   1 ----- 5
       box.max};
+  // clang-format on
 
 #define tri(i0, i1, i2) verts[i0], verts[i1], verts[i2]
-
   // TODO: Use vertex indices in Geometry.
   const vec3 tris[36] = {// Front.
                          tri(1, 5, 7), tri(1, 7, 3),
@@ -151,24 +173,84 @@ void gfx_imm_draw_aabb(ImmRenderer* renderer, aabb3 box) {
                          tri(3, 7, 6), tri(3, 6, 2),
                          // Bottom.
                          tri(0, 4, 5), tri(0, 5, 1)};
+#undef tri
 
   gfx_imm_draw_triangles(renderer, tris, 12);
 }
 
+// Load the top of the matrix stack into the shader.
+static void update_shader_model_matrix(ImmRenderer* renderer) {
+  assert(renderer);
+  imm_renderer_flush(renderer);
+  gfx_set_mat4_uniform(
+      renderer->shader, "Model",
+      &renderer->matrix_stack[renderer->stack_pointer]);
+}
+
+void gfx_imm_load_identity(ImmRenderer* renderer) {
+  assert(renderer);
+  renderer->matrix_stack[0] = mat4_id();
+  renderer->stack_pointer   = 0;
+  update_shader_model_matrix(renderer);
+}
+
+void gfx_imm_push_matrix(ImmRenderer* renderer, const mat4* matrix) {
+  assert(renderer);
+  assert(matrix);
+  assert(renderer->stack_pointer >= 0);
+  assert(renderer->stack_pointer < IMM_MAX_NUM_MATRICES); // TODO: hard assert.
+
+  renderer->matrix_stack[renderer->stack_pointer + 1] =
+      mat4_mul(*matrix, renderer->matrix_stack[renderer->stack_pointer]);
+  renderer->stack_pointer += 1;
+
+  update_shader_model_matrix(renderer);
+}
+
+void gfx_imm_pop_matrix(ImmRenderer* renderer) {
+  assert(renderer);
+  assert(renderer->stack_pointer > 0); // TODO: hard assert.
+
+  // For debugging, zero out the matrix stack as matrices are popped out.
+  memset(
+      &renderer->matrix_stack[renderer->stack_pointer], 0,
+      sizeof(renderer->matrix_stack[0]));
+
+  renderer->stack_pointer -= 1;
+
+  update_shader_model_matrix(renderer);
+}
+
+void gfx_imm_translate(ImmRenderer* renderer, vec3 offset) {
+  assert(renderer);
+  const mat4 mat = mat4_translate(offset);
+  gfx_imm_push_matrix(renderer, &mat);
+}
+
 void gfx_imm_set_camera(ImmRenderer* renderer, const Camera* camera) {
   assert(renderer);
   assert(renderer->shader);
   imm_renderer_flush(renderer);
-  const mat4 modelview = spatial3_inverse_transform(&camera->spatial);
-  const mat4 mvp       = mat4_mul(camera->projection, modelview);
-  gfx_set_mat4_uniform(renderer->shader, "ViewProjection", &mvp);
+  const mat4 view      = spatial3_inverse_transform(&camera->spatial);
+  const mat4 view_proj = mat4_mul(camera->projection, view);
+  gfx_imm_set_view_projection_matrix(renderer, &view_proj);
 }
 
 void gfx_imm_set_model_matrix(ImmRenderer* renderer, const mat4* model) {
   assert(renderer);
   assert(model);
   imm_renderer_flush(renderer);
-  gfx_set_mat4_uniform(renderer->shader, "Model", model);
+  renderer->matrix_stack[0] = mat4_id();
+  renderer->stack_pointer   = 0;
+  update_shader_model_matrix(renderer);
+}
+
+void gfx_imm_set_view_projection_matrix(
+    ImmRenderer* renderer, const mat4* view_proj) {
+  assert(renderer);
+  assert(renderer->shader);
+  imm_renderer_flush(renderer);
+  gfx_set_mat4_uniform(renderer->shader, "ViewProjection", view_proj);
 }
 
 void gfx_imm_set_colour(ImmRenderer* renderer, vec4 colour) {
diff --git a/gfx/src/renderer/imm_renderer_impl.h b/gfx/src/renderer/imm_renderer_impl.h
index 6f4b818..7769855 100644
--- a/gfx/src/renderer/imm_renderer_impl.h
+++ b/gfx/src/renderer/imm_renderer_impl.h
@@ -3,6 +3,7 @@
 #include <gfx/renderer.h>
 #include <gfx/sizes.h>
 
+#include <math/mat4.h>
 #include <math/vec3.h>
 
 #include <stdbool.h>
@@ -26,6 +27,11 @@ typedef struct ImmRenderer {
     bool wireframe : 1;
   } flags;
   vec3 triangle_verts[IMM_MAX_NUM_TRIANGLES * 3];
+  // Matrix stack contains pre-multiplied matrices.
+  // It is also never empty. The top of the stack is an identity matrix when the
+  // stack is "empty" from the user's perspective.
+  mat4 matrix_stack[IMM_MAX_NUM_MATRICES];
+  int  stack_pointer;
 } ImmRenderer;
 
 /// Create a new immediate mode renderer.