Create and clear offscreen texture

glest.cabal

@@ -70,6 +70,7 @@ library
     containers,
     exceptions,
     filepath,
+    gl,
     inline-c,
     mtl,
     network,

src/Glest/Renderer.hs

@@ -2,8 +2,63 @@ module Glest.Renderer (
   testRenderer
 ) where
 
+import Foreign
 import Glest.Egl
+import Graphics.GL.Embedded20
+import Graphics.GL.Types
+import Language.C.Inline (withPtr_)
 import Quasar.Prelude
 
 testRenderer :: IO ()
-testRenderer = initializeEgl
+testRenderer = do
+  initializeEgl
+  renderToDmabuf
+
+renderToDmabuf :: IO ()
+renderToDmabuf = do
+  texture <- genTexture
+  glBindTexture GL_TEXTURE_2D texture
+  let
+    width = 512
+    height = 512
+  glTexImage2D GL_TEXTURE_2D 0 GL_RGBA width height 0 GL_RGBA GL_UNSIGNED_BYTE nullPtr
+  glTexParameteri GL_TEXTURE_2D GL_TEXTURE_MIN_FILTER GL_NEAREST
+  glTexParameteri GL_TEXTURE_2D GL_TEXTURE_MAG_FILTER GL_NEAREST
+
+  framebuffer <- alloca \ptr -> do
+    glGenFramebuffers 1 ptr
+    peek ptr
+  traceIO $ mconcat ["Generated framebuffer@", show framebuffer]
+
+  glBindFramebuffer GL_FRAMEBUFFER framebuffer
+  glFramebufferTexture2D GL_FRAMEBUFFER GL_COLOR_ATTACHMENT0 GL_TEXTURE_2D texture 0
+
+  glClearColor 1 0 1 1
+  glClear GL_COLOR_BUFFER_BIT
+
+  logErrors
+
+
+genTexture :: IO GLuint
+genTexture = do
+  texture <- alloca \ptr -> do
+    glGenTextures 1 ptr
+    peek ptr
+  traceIO $ mconcat ["Generated texture@", show texture]
+  pure texture
+
+logErrors :: IO ()
+logErrors = do
+  err <- glGetError
+  unless (err == GL_NO_ERROR) do
+    traceIO $ errorMessage err
+    logErrors
+
+errorMessage :: GLenum -> String
+errorMessage GL_NO_ERROR = "GL_NO_ERROR"
+errorMessage GL_INVALID_ENUM = "GL_INVALID_ENUM"
+errorMessage GL_INVALID_VALUE = "GL_INVALID_VALUE"
+errorMessage GL_INVALID_OPERATION = "GL_INVALID_OPERATION"
+errorMessage GL_INVALID_FRAMEBUFFER_OPERATION = "GL_INVALID_FRAMEBUFFER_OPERATION"
+errorMessage GL_OUT_OF_MEMORY = "GL_OUT_OF_MEMORY"
+errorMessage _ = "Invalid GL error number"