Implementation of mesh:attachAttributes(), with optional instance divisor

Some features remain to be implemented, these are marked with TODOs.

Currently it is not allowed to attach a mesh which itself has attachments.

src/api/types/mesh.c

@@ -229,6 +229,20 @@ int l_lovrMeshSetMaterial(lua_State* L) {
   return 0;
 }
 
+int l_lovrMeshAttachAttributes(lua_State* L) {
+  Mesh* attachTo = luax_checktype(L, 1, Mesh);
+  Mesh* attachThis = luax_checktype(L, 2, Mesh);
+  int instanceDivisor = luaL_optnumber(L, 3, 0);
+  // TODO: Check attribute name(s) in 4th argument and if present only attach those
+
+  VertexFormat* format = &attachThis->vertexData->format;
+  for(int c = 0; c < format->count; c++) {
+    lovrMeshAttach(attachTo, attachThis, c, instanceDivisor);
+  }
+
+  return 0;
+}
+
 const luaL_Reg lovrMesh[] = {
   { "drawInstanced", l_lovrMeshDrawInstanced },
   { "draw", l_lovrMeshDraw },
@@ -249,5 +263,6 @@ const luaL_Reg lovrMesh[] = {
   { "setDrawRange", l_lovrMeshSetDrawRange },
   { "getMaterial", l_lovrMeshGetMaterial },
   { "setMaterial", l_lovrMeshSetMaterial },
+  { "attachAttributes", l_lovrMeshAttachAttributes },
   { NULL, NULL }
 };

src/graphics/mesh.c

@@ -4,6 +4,36 @@
 #include <stdlib.h>
 #include <stdio.h>
 
+static void lovrMeshBindAttribute(Shader* shader, Mesh *mesh, VertexFormat *format, int i, bool enabled, int divisor) {
+  Attribute attribute = format->attributes[i];
+  int location = lovrShaderGetAttributeId(shader, attribute.name);
+
+  if (location >= 0) {
+    if (enabled) {
+      glEnableVertexAttribArray(location);
+
+      GLenum glType;
+      switch (attribute.type) {
+        case ATTR_FLOAT: glType = GL_FLOAT; break;
+        case ATTR_BYTE: glType = GL_UNSIGNED_BYTE; break;
+        case ATTR_INT: glType = GL_UNSIGNED_INT; break;
+      }
+
+      // Divisor lives in the VAO and the VAO is per-mesh, so the only reason we would need to set a zero divisor for an attribute is if a nonzero divisor attribute is attached then disabled, and a zero divisor attribute is enabled afterward in its place. Nonzero attachments length is used to determine there is a risk this has happened.
+      if (divisor || mesh->attachments.length)
+        glVertexAttribDivisor(location, divisor);
+
+      if (attribute.type == ATTR_INT) {
+        glVertexAttribIPointer(location, attribute.count, glType, format->stride, (void*) attribute.offset);
+      } else {
+        glVertexAttribPointer(location, attribute.count, glType, GL_TRUE, format->stride, (void*) attribute.offset);
+      }
+    } else {
+      glDisableVertexAttribArray(location);
+    }
+  }
+}
+
 static void lovrMeshBindAttributes(Mesh* mesh) {
   Shader* shader = lovrGraphicsGetActiveShader();
   if (shader == mesh->lastShader && !mesh->attributesDirty) {
@@ -14,28 +44,15 @@ static void lovrMeshBindAttributes(Mesh* mesh) {
 
   VertexFormat* format = &mesh->vertexData->format;
   for (int i = 0; i < format->count; i++) {
-    Attribute attribute = format->attributes[i];
-    int location = lovrShaderGetAttributeId(shader, attribute.name);
+    lovrMeshBindAttribute(shader, mesh, format, i, mesh->enabledAttributes & (1 << i), 0);
+  }
 
-    if (location >= 0) {
-      if (mesh->enabledAttributes & (1 << i)) {
-        glEnableVertexAttribArray(location);
-
-        GLenum glType;
-        switch (attribute.type) {
-          case ATTR_FLOAT: glType = GL_FLOAT; break;
-          case ATTR_BYTE: glType = GL_UNSIGNED_BYTE; break;
-          case ATTR_INT: glType = GL_UNSIGNED_INT; break;
-        }
-
-        if (attribute.type == ATTR_INT) {
-          glVertexAttribIPointer(location, attribute.count, glType, format->stride, (void*) attribute.offset);
-        } else {
-          glVertexAttribPointer(location, attribute.count, glType, GL_TRUE, format->stride, (void*) attribute.offset);
-        }
-      } else {
-        glDisableVertexAttribArray(location);
-      }
+  {
+    int i; MeshAttachment attachment;
+    vec_foreach(&mesh->attachments, attachment, i) {
+      lovrGraphicsBindVertexBuffer(attachment.mesh->vbo);
+      // TODO: Allow disabling of attached attributes?
+      lovrMeshBindAttribute(shader, attachment.mesh, &attachment.mesh->vertexData->format, attachment.attribute, true, attachment.instanceDivisor);
     }
   }
 
@@ -70,8 +87,11 @@ Mesh* lovrMeshCreate(uint32_t count, VertexFormat* format, MeshDrawMode drawMode
   mesh->vbo = 0;
   mesh->ibo = 0;
   mesh->material = NULL;
+  vec_init(&mesh->attachments);
   mesh->lastShader = NULL;
 
+  mesh->isAnAttachment = false;
+
   glGenBuffers(1, &mesh->vbo);
   glGenBuffers(1, &mesh->ibo);
   lovrGraphicsBindVertexBuffer(mesh->vbo);
@@ -88,6 +108,15 @@ void lovrMeshDestroy(void* ref) {
   glDeleteBuffers(1, &mesh->vbo);
   glDeleteBuffers(1, &mesh->ibo);
   glDeleteVertexArrays(1, &mesh->vao);
+
+  {
+    int i; MeshAttachment attachment;
+    vec_foreach(&mesh->attachments, attachment, i) {
+      lovrRelease(attachment.mesh);
+    }
+  }
+  vec_deinit(&mesh->attachments);
+  
   free(mesh->indices.raw);
   free(mesh);
 }
@@ -268,3 +297,14 @@ void lovrMeshUnmap(Mesh* mesh) {
   glUnmapBuffer(GL_ARRAY_BUFFER);
 #endif
 }
+
+void lovrMeshAttach(Mesh *attachTo, Mesh* attachThis, int attribute, int instanceDivisor)
+{
+  lovrAssert(!attachTo->isAnAttachment, "Attempted to attach to a mesh which is an attachment itself");
+  lovrAssert(!attachThis->attachments.length, "Attempted to attach a mesh which has attachments itself");
+
+  MeshAttachment attachment = {attachThis, attribute, instanceDivisor};
+  attachThis->isAnAttachment = true;
+  lovrRetain(attachThis);
+  vec_push(&attachTo->attachments, attachment);
+}

src/graphics/mesh.h

@@ -22,7 +22,17 @@ typedef enum {
   MESH_STREAM = GL_STREAM_DRAW
 } MeshUsage;
 
+typedef struct Mesh Mesh;
+
 typedef struct {
+  Mesh *mesh;
+  int attribute;
+  int instanceDivisor;
+} MeshAttachment;
+
+typedef vec_t(MeshAttachment) vec_meshattachment_t;
+
+struct Mesh {
   Ref ref;
   VertexData* vertexData;
   IndexPointer indices;
@@ -43,7 +53,9 @@ typedef struct {
   GLuint ibo;
   Material* material;
   Shader* lastShader;
-} Mesh;
+  vec_meshattachment_t attachments;
+  bool isAnAttachment;
+};
 
 Mesh* lovrMeshCreate(uint32_t count, VertexFormat* format, MeshDrawMode drawMode, MeshUsage usage);
 void lovrMeshDestroy(void* ref);
@@ -64,3 +76,4 @@ Material* lovrMeshGetMaterial(Mesh* mesh);
 void lovrMeshSetMaterial(Mesh* mesh, Material* material);
 VertexPointer lovrMeshMap(Mesh* mesh, int start, size_t count, bool read, bool write);
 void lovrMeshUnmap(Mesh* mesh);
+void lovrMeshAttach(Mesh *attachTo, Mesh* attachThis, int attribute, int instanceDivisor);