Allow creation of Geometry from literal arrays. Simplify Buffer.

4 files changed, 222 insertions, 101 deletions

diff --git a/Spear/Render/Core/Buffer.hs b/Spear/Render/Core/Buffer.hs
index 6f1e355..a4e98a4 100644
--- a/Spear/Render/Core/Buffer.hs
+++ b/Spear/Render/Core/Buffer.hs
@@ -13,8 +13,8 @@ import           Spear.Game
 import           Spear.Math.Vector
 import           Spear.Render.Core.State
 
-import           Control.Monad           (void)
-import           Data.HashMap            as HashMap
+import           Control.Monad           (unless, void)
+import qualified Data.HashMap            as HashMap
 import           Data.Word
 import           Foreign.C.Types
 import           Foreign.Marshal.Alloc
@@ -29,6 +29,7 @@ data BufferData
   = BufferDataUntyped (Ptr Word8) GLuint
   | BufferDataVec2    [Vector2]
   | BufferDataVec3    [Vector3]
+  | BufferDataVec4    [Vector4]
   | BufferDataFloat   [Float]
   | BufferDataU8      [Word8]
   | BufferDataU16     [Word16]
@@ -36,7 +37,6 @@ data BufferData
 
 data BufferDesc = BufferDesc
   { bufferDescUsage :: BufferUsage
-  , bufferDescType  :: BufferType
   , bufferDescData  :: BufferData
   }
 
@@ -52,10 +52,10 @@ makeBufferAndView desc = do
     }
 
 makeBuffer :: BufferDesc -> Game RenderCoreState Buffer
-makeBuffer (BufferDesc usage bufferType bufferData) = do
+makeBuffer (BufferDesc usage bufferData) = do
   handle <- gameIO $ alloca $ \ptr -> glGenBuffers 1 ptr >> peek ptr
   resourceKey <- register $ deleteBuffer' handle
-  let buffer = Buffer handle resourceKey bufferType usage
+  let buffer = Buffer handle resourceKey usage
   gameIO $ updateBuffer buffer bufferData
   modifyGameState (\state -> state {
     buffers = HashMap.insert handle buffer (buffers state) })
@@ -71,12 +71,10 @@ deleteBuffer buffer = do
 -- TODO: use glBufferSubData for updates.
 updateBuffer :: Buffer -> BufferData -> IO ()
 updateBuffer buffer bufferData =
-  case bufferData of
-    BufferUninitialized -> return ()
-    _ -> do
-      glBindBuffer GL_ARRAY_BUFFER (bufferHandle buffer)
-      uploadData (bufferUsage buffer) bufferData
-      glBindBuffer GL_ARRAY_BUFFER 0
+  unless (bufferEmpty bufferData) $ do
+    glBindBuffer GL_ARRAY_BUFFER (bufferHandle buffer)
+    uploadData (bufferUsage buffer) bufferData
+    glBindBuffer GL_ARRAY_BUFFER 0
 
 -- Private
 
@@ -87,26 +85,35 @@ deleteBuffer' handle = alloca $ \ptr -> do
 
 uploadData :: BufferUsage -> BufferData -> IO ()
 uploadData usage bufferData = case bufferData of
-  BufferDataUntyped ptr sizeBytes -> do
+  BufferDataUntyped ptr sizeBytes ->
     glBufferData GL_ARRAY_BUFFER (fromIntegral sizeBytes) (unsafeCoerce ptr) usage'
-  BufferDataVec2 vec2s -> withArrayLen vec2s $ \numElems ptr -> do
-    let sizeBytes = numElems * sizeOf (undefined :: Vector2)
+  BufferDataVec2 vec2s -> withArrayLen vec2s $ \numElems ptr ->
     glBufferData GL_ARRAY_BUFFER (fromIntegral sizeBytes) ptr usage'
-  BufferDataVec3 vec3s -> withArrayLen vec3s $ \numElems ptr -> do
-    let sizeBytes = numElems * sizeOf (undefined :: Vector3)
+  BufferDataVec3 vec3s -> withArrayLen vec3s $ \numElems ptr ->
     glBufferData GL_ARRAY_BUFFER (fromIntegral sizeBytes) ptr usage'
-  BufferDataFloat floats -> withArrayLen floats $ \numElems ptr -> do
-    let sizeBytes = numElems * sizeOf (undefined :: CFloat)
+  BufferDataVec4 vec4s -> withArrayLen vec4s $ \numElems ptr ->
     glBufferData GL_ARRAY_BUFFER (fromIntegral sizeBytes) ptr usage'
-  BufferDataU8 ints -> withArrayLen ints $ \numElems ptr -> do
-    let sizeBytes = numElems * sizeOf (undefined :: Word8)
+  BufferDataFloat floats -> withArrayLen floats $ \numElems ptr ->
     glBufferData GL_ARRAY_BUFFER (fromIntegral sizeBytes) ptr usage'
-  BufferDataU16 ints -> withArrayLen ints $ \numElems ptr -> do
-    let sizeBytes = numElems * sizeOf (undefined :: Word16)
+  BufferDataU8 ints -> withArrayLen ints $ \numElems ptr ->
+    glBufferData GL_ARRAY_BUFFER (fromIntegral sizeBytes) ptr usage'
+  BufferDataU16 ints -> withArrayLen ints $ \numElems ptr ->
     glBufferData GL_ARRAY_BUFFER (fromIntegral sizeBytes) ptr usage'
   BufferUninitialized ->
     return ()
-  where usage' = toGLUsage usage
+  where
+    usage' = toGLUsage usage
+    sizeBytes = bufferDataSizeBytes bufferData
+
+bufferEmpty :: BufferData -> Bool
+bufferEmpty (BufferDataUntyped ptr sizeBytes) = sizeBytes /= 0
+bufferEmpty (BufferDataVec2    list)          = null list
+bufferEmpty (BufferDataVec3    list)          = null list
+bufferEmpty (BufferDataVec4    list)          = null list
+bufferEmpty (BufferDataFloat   list)          = null list
+bufferEmpty (BufferDataU8      list)          = null list
+bufferEmpty (BufferDataU16     list)          = null list
+bufferEmpty  BufferUninitialized              = True
 
 toGLUsage :: BufferUsage -> GLenum
 toGLUsage BufferStatic  = GL_STATIC_DRAW
@@ -117,6 +124,7 @@ bufferDataSizeBytes bufferData = case bufferData of
   BufferDataUntyped ptr sizeBytes -> sizeBytes
   BufferDataVec2    vec2s         -> fromIntegral $ length vec2s  * sizeOf (undefined :: Vector2)
   BufferDataVec3    vec3s         -> fromIntegral $ length vec3s  * sizeOf (undefined :: Vector3)
+  BufferDataVec4    vec4s         -> fromIntegral $ length vec4s  * sizeOf (undefined :: Vector4)
   BufferDataFloat   floats        -> fromIntegral $ length floats * 4
   BufferDataU8      bytes         -> fromIntegral $ length bytes
   BufferDataU16     words         -> fromIntegral $ length words  * 2
diff --git a/Spear/Render/Core/Geometry.hs b/Spear/Render/Core/Geometry.hs
index aa0dfe5..6c05b38 100644
--- a/Spear/Render/Core/Geometry.hs
+++ b/Spear/Render/Core/Geometry.hs
@@ -1,6 +1,12 @@
 module Spear.Render.Core.Geometry
 (
-  newGeometryDesc
+  GeometryDesc(..)
+, VertexData(..)
+, Positions(..)
+, Indices(..)
+, Weights(..)
+, GeometryUsage(..)
+, newGeometryDesc
 , makeGeometry
 , deleteGeometry
 , renderGeometry
@@ -10,19 +16,58 @@ where
 
 
 import           Spear.Game
-import           Spear.Math.Vector.Vector3
+import           Spear.Math.Vector
 import           Spear.Render.Core.Buffer
 import           Spear.Render.Core.Constants
 import           Spear.Render.Core.State
 
 import           Data.HashMap                as HashMap
 import           Data.IORef
+import           Data.Maybe                  (fromJust)
+import           Data.Word
 import           Foreign.Marshal.Alloc
 import           Foreign.Storable
 import           Graphics.GL.Core46
 import           Unsafe.Coerce
 
 
+data VertexData v
+  = FromView (BufferView v)
+  | FromList [v]
+
+data Positions
+  = Positions2d (VertexData Vector2)
+  | Positions3d (VertexData Vector3)
+
+data Indices
+  = IndicesU8  (VertexData Word8)
+  | IndicesU16 (VertexData Word16)
+
+data Weights
+  = WeightsU8    (VertexData Word8)
+  | WeightsU16   (VertexData Word16)
+  | WeightsFloat (VertexData Float)
+
+data GeometryUsage
+  = GeometryStatic
+  | GeometryDynamic
+
+-- | A geometry descriptor.
+data GeometryDesc = GeometryDesc
+  { positions     :: Maybe Positions -- Convenient for the empty descriptor.
+  , normals       :: Maybe (VertexData Vector3)
+  , tangents      :: Maybe (VertexData Vector4)
+  , texcoords     :: Maybe (VertexData Vector4)
+  , joints        :: Maybe Indices
+  , weights       :: Maybe Weights
+  , indices       :: Maybe Indices
+  , numVerts      :: GLsizei
+  , numIndices    :: GLsizei
+  , primitiveType :: PrimitiveType
+  , geometryUsage :: GeometryUsage
+  }
+
+
 newGeometryDesc :: GeometryDesc
 newGeometryDesc = GeometryDesc
   { positions     = Nothing
@@ -35,19 +80,21 @@ newGeometryDesc = GeometryDesc
   , numVerts      = 0
   , numIndices    = 0
   , primitiveType = Triangles
+  , geometryUsage = GeometryStatic
   }
 
 
 makeGeometry :: GeometryDesc -> Game RenderCoreState Geometry
 makeGeometry desc = do
+  gdata  <- geometryDescToData desc
   handle <- gameIO $ alloca $ \ptr -> glGenVertexArrays 1 ptr >> peek ptr
   gameIO $ do
     glBindVertexArray handle
-    configureVertexAttributes desc
+    configureVertexAttributes gdata
     glBindVertexArray 0
-  descRef <- gameIO $ newIORef desc
+  gdataRef <- gameIO $ newIORef gdata
   resourceKey <- register $ deleteGeometry' handle
-  let geometry = Geometry handle resourceKey descRef
+  let geometry = Geometry handle resourceKey gdataRef
   modifyGameState (\state -> state {
     geometries = HashMap.insert handle geometry (geometries state) })
   return geometry
@@ -60,39 +107,120 @@ deleteGeometry geometry = do
 
 renderGeometry :: Geometry -> IO ()
 renderGeometry geometry = do
-  desc <- readIORef (geometryDesc geometry)
-  let mode = toGLPrimitiveType $ primitiveType desc
+  gdata <- readIORef (geometryData geometry)
+  let mode = toGLPrimitiveType $ geometryPrimitiveType gdata
   glBindVertexArray (geometryVao geometry)
-  case indices desc of
-    (Just (IndicesU8 view))  -> renderIndexed view mode (numIndices desc) GL_UNSIGNED_BYTE
-    (Just (IndicesU16 view)) -> renderIndexed view mode (numIndices desc) GL_UNSIGNED_SHORT
-    Nothing                  -> glDrawArrays mode 0 (numVerts desc)
+  case vertexIndices gdata of
+    (Just (VertexIndicesU8  view)) ->
+      renderIndexed view mode (geometryNumIndices gdata) GL_UNSIGNED_BYTE
+    (Just (VertexIndicesU16 view)) ->
+      renderIndexed view mode (geometryNumIndices gdata) GL_UNSIGNED_SHORT
+    Nothing                  ->
+      glDrawArrays mode 0 (geometryNumVerts gdata)
   glBindVertexArray 0
 
 -- Functions for updating dynamic geometry.
 
 setPositions :: Geometry -> [Vector3] -> IO ()
 setPositions geometry vectors = do
-  desc <- readIORef $ geometryDesc geometry
-  case positions desc of
-    Just (Positions3d view) -> do
+  gdata <- readIORef $ geometryData geometry
+  case vertexPositions gdata of
+    VertexPositions3d view -> do
       updateBuffer (bufferViewBuffer view) (BufferDataVec3 vectors)
-      updateGeometry geometry $ \desc -> desc {
-        numVerts = fromIntegral . length $ vectors
+      updateGeometry geometry $ \gdata -> gdata {
+        geometryNumVerts = fromIntegral . length $ vectors
       }
     _ -> putStrLn "setPositions ERROR" -- TODO: handle gracefully
 
 -- Private
 
+geometryDescToData :: GeometryDesc -> Game RenderCoreState GeometryData
+geometryDescToData desc =
+  let
+    bufferUsage = toBufferUsage (geometryUsage desc)
+    toBufferUsage GeometryStatic  = BufferStatic
+    toBufferUsage GeometryDynamic = BufferDynamic
+    -- Maybe handling.
+    convert :: (a -> Game RenderCoreState b) -> Maybe a -> Game RenderCoreState (Maybe b)
+    convert f value = case value of
+      Nothing -> return Nothing
+      Just x  -> Just <$> f x
+    -- 2d vectors
+    convert2d :: VertexData Vector2 -> Game RenderCoreState (BufferView Vector2)
+    convert2d (FromView view)  = return view
+    convert2d (FromList vec2s) = makeBufferAndView $
+      BufferDesc bufferUsage (BufferDataVec2 vec2s)
+    -- 3d vectors
+    convert3d :: VertexData Vector3 -> Game RenderCoreState (BufferView Vector3)
+    convert3d (FromView view)  = return view
+    convert3d (FromList vec3s) = makeBufferAndView $
+      BufferDesc bufferUsage (BufferDataVec3 vec3s)
+    -- 4d vectors
+    convert4d :: VertexData Vector4 -> Game RenderCoreState (BufferView Vector4)
+    convert4d (FromView view)  = return view
+    convert4d (FromList vec4s) = makeBufferAndView $
+      BufferDesc bufferUsage (BufferDataVec4 vec4s)
+    -- U8
+    convertU8 :: VertexData Word8 -> Game RenderCoreState (BufferView Word8)
+    convertU8 (FromView view) = return view
+    convertU8 (FromList list) = makeBufferAndView
+      (BufferDesc BufferStatic (BufferDataU8  $ fromIntegral <$> list))
+    -- U16
+    convertU16 :: VertexData Word16 -> Game RenderCoreState (BufferView Word16)
+    convertU16 (FromView view) = return view
+    convertU16 (FromList list) = makeBufferAndView
+      (BufferDesc BufferStatic (BufferDataU16 $ fromIntegral <$> list))
+    -- Floats
+    convertFloat :: VertexData Float -> Game RenderCoreState (BufferView Float)
+    convertFloat (FromView view) = return view
+    convertFloat (FromList list) = makeBufferAndView
+      (BufferDesc BufferStatic (BufferDataFloat list))
+    -- Positions
+    convertPositions :: Positions -> Game RenderCoreState VertexPositions
+    convertPositions (Positions2d positions) = VertexPositions2d <$> convert2d positions
+    convertPositions (Positions3d positions) = VertexPositions3d <$> convert3d positions
+    -- Joints
+    convertJoints :: Indices -> Game RenderCoreState VertexJoints
+    convertJoints (IndicesU8  joints) = VertexJointsU8  <$> convertU8  joints
+    convertJoints (IndicesU16 joints) = VertexJointsU16 <$> convertU16 joints
+    -- Weights
+    convertWeights :: Weights -> Game RenderCoreState VertexWeights
+    convertWeights (WeightsU8    weights) = VertexWeightsU8    <$> convertU8    weights
+    convertWeights (WeightsU16   weights) = VertexWeightsU16   <$> convertU16   weights
+    convertWeights (WeightsFloat weights) = VertexWeightsFloat <$> convertFloat weights
+    -- Indices
+    convertIndices :: Indices -> Game RenderCoreState VertexIndices
+    convertIndices (IndicesU8  indices) = VertexIndicesU8  <$> convertU8  indices
+    convertIndices (IndicesU16 indices) = VertexIndicesU16 <$> convertU16 indices
+  in do
+    vertexPositions       <- convertPositions (fromJust $ positions desc)
+    vertexNormals         <- convert convert3d      (normals desc)
+    vertexTangents        <- convert convert4d      (tangents desc)
+    vertexTexcoords       <- convert convert4d      (texcoords desc)
+    vertexJoints          <- convert convertJoints  (joints desc)
+    vertexWeights         <- convert convertWeights (weights desc)
+    vertexIndices         <- convert convertIndices (indices desc)
+    return $ GeometryData
+      vertexPositions
+      vertexNormals
+      vertexTangents
+      vertexTexcoords
+      vertexJoints
+      vertexWeights
+      vertexIndices
+      (numVerts desc)
+      (numIndices desc)
+      (primitiveType desc)
+
 deleteGeometry' :: GLenum -> IO ()
 deleteGeometry' handle = alloca $ \ptr -> do
   poke ptr handle
   glDeleteVertexArrays 1 ptr
 
-updateGeometry :: Geometry -> (GeometryDesc -> GeometryDesc) -> IO ()
+updateGeometry :: Geometry -> (GeometryData -> GeometryData) -> IO ()
 updateGeometry geometry update = do
-  desc <- readIORef $ geometryDesc geometry
-  writeIORef (geometryDesc geometry) (update desc)
+  gdata <- readIORef $ geometryData geometry
+  writeIORef (geometryData geometry) (update gdata)
 
 renderIndexed :: BufferView a -> GLenum -> GLsizei -> GLenum -> IO ()
 renderIndexed view mode numIndices indexElemSize = do
@@ -100,29 +228,28 @@ renderIndexed view mode numIndices indexElemSize = do
   glDrawElements mode numIndices GL_UNSIGNED_SHORT (unsafeCoerce $ bufferViewOffsetBytes view)
   glBindBuffer GL_ELEMENT_ARRAY_BUFFER 0
 
-configureVertexAttributes :: GeometryDesc -> IO ()
-configureVertexAttributes desc = do
-  case positions desc of
-    Just (Positions2d view) -> configureView view positionChannel 2 GL_FLOAT GL_FALSE
-    Just (Positions3d view) -> configureView view positionChannel 3 GL_FLOAT GL_FALSE
-    Nothing                 -> return ()
-  case normals desc of
+configureVertexAttributes :: GeometryData -> IO ()
+configureVertexAttributes gdata = do
+  case vertexPositions gdata of
+    VertexPositions2d view -> configureView view positionChannel 2 GL_FLOAT GL_FALSE
+    VertexPositions3d view -> configureView view positionChannel 3 GL_FLOAT GL_FALSE
+  case vertexNormals gdata of
     Just view -> configureView view normalChannel 3 GL_FLOAT GL_FALSE
     Nothing   -> return ()
-  case tangents desc of
+  case vertexTangents gdata of
     Just view -> configureView view tangentChannel 4 GL_FLOAT GL_FALSE
     Nothing   -> return ()
-  case texcoords desc of
+  case vertexTexcoords gdata of
     Just view -> configureView view texcoordsChannel 2 GL_FLOAT GL_FALSE
     Nothing   -> return ()
-  case joints desc of
-    Just (JointsU8 view)  -> configureView view jointsChannel 4 GL_UNSIGNED_BYTE  GL_FALSE
-    Just (JointsU16 view) -> configureView view jointsChannel 4 GL_UNSIGNED_SHORT GL_FALSE
+  case vertexJoints gdata of
+    Just (VertexJointsU8 view)  -> configureView view jointsChannel 4 GL_UNSIGNED_BYTE  GL_FALSE
+    Just (VertexJointsU16 view) -> configureView view jointsChannel 4 GL_UNSIGNED_SHORT GL_FALSE
     Nothing               -> return ()
-  case weights desc of
-    Just (WeightsU8    view) -> configureView view weightsChannel 4 GL_UNSIGNED_BYTE  GL_TRUE
-    Just (WeightsU16   view) -> configureView view weightsChannel 4 GL_UNSIGNED_SHORT GL_TRUE
-    Just (WeightsFloat view) -> configureView view weightsChannel 4 GL_FLOAT          GL_FALSE
+  case vertexWeights gdata of
+    Just (VertexWeightsU8    view) -> configureView view weightsChannel 4 GL_UNSIGNED_BYTE  GL_TRUE
+    Just (VertexWeightsU16   view) -> configureView view weightsChannel 4 GL_UNSIGNED_SHORT GL_TRUE
+    Just (VertexWeightsFloat view) -> configureView view weightsChannel 4 GL_FLOAT          GL_FALSE
     Nothing                  -> return ()
 
 -- TODO: Add the assertion:
diff --git a/Spear/Render/Core/State.hs b/Spear/Render/Core/State.hs
index 34b0732..f7e5627 100644
--- a/Spear/Render/Core/State.hs
+++ b/Spear/Render/Core/State.hs
@@ -11,15 +11,6 @@ import           Graphics.GL.Core46
 
 
 
-data BufferType
-  = BufferUntyped
-  | Buffer2d
-  | Buffer3d
-  | Buffer4d
-  | BufferFloat
-  | BufferU8
-  | BufferU16
-
 data BufferUsage
   = BufferStatic
   | BufferDynamic
@@ -28,7 +19,6 @@ data BufferUsage
 data Buffer = Buffer
   { bufferHandle   :: GLuint
   , bufferResource :: Resource
-  , bufferType     :: BufferType
   , bufferUsage    :: BufferUsage
   }
 
@@ -41,50 +31,49 @@ data BufferView a = BufferView
   }
 
 
-data Positions
-  = Positions2d (BufferView Vector2)
-  | Positions3d (BufferView Vector3)
+data VertexPositions
+  = VertexPositions2d (BufferView Vector2)
+  | VertexPositions3d (BufferView Vector3)
 
-data Joints
-  = JointsU8  (BufferView Word8)
-  | JointsU16 (BufferView Word16)
+data VertexJoints
+  = VertexJointsU8  (BufferView Word8)
+  | VertexJointsU16 (BufferView Word16)
 
-data Weights
-  = WeightsU8    (BufferView Word8)
-  | WeightsU16   (BufferView Word16)
-  | WeightsFloat (BufferView Float)
+data VertexWeights
+  = VertexWeightsU8    (BufferView Word8)
+  | VertexWeightsU16   (BufferView Word16)
+  | VertexWeightsFloat (BufferView Float)
 
-data Indices
-  = IndicesU8  (BufferView Word8)
-  | IndicesU16 (BufferView Word16)
+data VertexIndices
+  = VertexIndicesU8  (BufferView Word8)
+  | VertexIndicesU16 (BufferView Word16)
 
 data PrimitiveType
   = Triangles
   | TriangleFan
   | TriangleStrip
 
--- | A geometry descriptor.
-data GeometryDesc = GeometryDesc
-  { positions     :: Maybe Positions -- Convenient for the empty descriptor.
-  , normals       :: Maybe (BufferView Vector3)
-  , tangents      :: Maybe (BufferView Vector4)
-  , texcoords     :: Maybe (BufferView Vector4)
-  , joints        :: Maybe Joints
-  , weights       :: Maybe Weights
-  , indices       :: Maybe Indices
-  , numVerts      :: GLsizei
-  , numIndices    :: GLsizei
-  , primitiveType :: PrimitiveType
+data GeometryData = GeometryData
+  { vertexPositions       :: VertexPositions
+  , vertexNormals         :: Maybe (BufferView Vector3)
+  , vertexTangents        :: Maybe (BufferView Vector4)
+  , vertexTexcoords       :: Maybe (BufferView Vector4)
+  , vertexJoints          :: Maybe VertexJoints
+  , vertexWeights         :: Maybe VertexWeights
+  , vertexIndices         :: Maybe VertexIndices
+  , geometryNumVerts      :: GLsizei
+  , geometryNumIndices    :: GLsizei
+  , geometryPrimitiveType :: PrimitiveType
   }
 
 -- | A piece of renderable geometry.
 --
--- Since dynamic geometry can be mutated, the descriptor is stored as an IORef
--- so that its state cannot become stale after an update.
+-- Since dynamic geometry can be mutated, the data is stored as an IORef so that
+-- its state cannot become stale after an update.
 data Geometry = Geometry
   { geometryVao      :: GLuint
   , geometryResource :: Resource
-  , geometryDesc     :: IORef GeometryDesc
+  , geometryData     :: IORef GeometryData
   }
 
 
diff --git a/Spear/Render/Immediate.hs b/Spear/Render/Immediate.hs
index ca5d5c5..44fe7a6 100644
--- a/Spear/Render/Immediate.hs
+++ b/Spear/Render/Immediate.hs
@@ -54,13 +54,10 @@ newImmRenderer = do
     (ShaderFromFile "/home/jeanne/src/gfx/gfx/shaders/immediate_mode.frag") []
   shader <- compileShaderProgram [vs, ps]
 
-  -- TODO: Make 'makeGeometry' easier to use. GeometryDesc should be able to
-  -- take (possibly empty) lists as inputs.
-  positions <- makeBufferAndView $
-    BufferDesc BufferDynamic Buffer3d BufferUninitialized
   triangles <- makeGeometry $ newGeometryDesc
-    { positions     = Just (Positions3d positions)
+    { positions     = Just (Positions3d (FromList []))
     , primitiveType = Triangles
+    , geometryUsage = GeometryDynamic
     }
 
   return ImmRenderState