Screen: Add newFramebufferScreen, newTextureScreen, setTexture.

src/graphics/framebuffer.nim

@@ -50,6 +50,7 @@ proc newFramebuffer*(engine: MyouEngine,
         texture: Texture = nil,
     ): Framebuffer
 proc set_attachments(self: Framebuffer; layer, mipmap_level: int)
+proc set_texture*(self: Framebuffer, texture: Texture)
 proc enable*(self: Framebuffer, rect = none((int32,int32,int32,int32)),
         layer = -1, mipmap_level = 0, mark_textures = true): Framebuffer {.discardable.}
 proc clear*(self: Framebuffer, color = vec4(0,0,0,0), clear_color = true, clear_depth = true, layer = -1) {.inline.}
@@ -174,6 +175,12 @@ proc set_attachments(self: Framebuffer; layer, mipmap_level: int) =
                 glFramebufferTexture2D(GL_FRAMEBUFFER, attachments[i], 
                     tex.storage.target, tex.storage.tex.GLuint, mipmap_level.GLint)
 
+proc set_texture*(self: Framebuffer, texture: Texture) =
+    if active_buffer == self:
+        self.disable()
+    self.texture = texture
+    self.current_mipmap_level = -1 # this forces attachment
+
 proc enable*(self: Framebuffer, rect = none((int32,int32,int32,int32)),
         layer = -1, mipmap_level = 0, mark_textures = true): Framebuffer {.discardable.} =
     self.has_mipmap = false

src/screen.nim

@@ -30,10 +30,19 @@
 # License. If you do not delete the provisions above, a recipient may use your
 # version of this file under either the CPAL or the [AGPL-3] License.
 
+## In the engine, a screen represents e.g. a screen, a window, a canvas, or a
+## render-to-texture framebuffer, with one or more viewports where stuff is drawn
+## from the perspective of a camera in a scene.
+## 
+## If it's a screen, window or canvas, it's also the receiver of user events.
+
 import ./types
 
 # Forward declarations
 proc newScreen*(engine: MyouEngine, width, height: int32, title: string): Screen
+proc newFramebufferScreen*(engine: MyouEngine, fb: Framebuffer): Screen
+proc newTextureScreen*(engine: MyouEngine, texture: Texture,  depth_type: FramebufferDepthType = DepthRenderBuffer, depth_format = Depth_u24): Screen
+proc setTexture*(self: Screen, texture: Texture)
 proc destroy*(self: Screen)
 proc resize*(self: Screen, width, height: int32, orientation = self.orientation)
 proc add_viewport*(self: Screen, camera: Camera)
@@ -73,6 +82,42 @@ proc newScreen*(engine: MyouEngine, width, height: int32, title: string): Screen
     result.frame_interval = 1
     result.display_scale = 1.0
 
+proc newFramebufferScreen*(engine: MyouEngine, fb: Framebuffer): Screen =
+    ## Creates a new virtual screen from a framebuffer to render to it.
+    
+    result = new Screen
+    result.engine = engine
+    result.width = fb.width.int32
+    result.height = fb.height.int32
+    result.framebuffer = fb
+    result.enabled = true
+    engine.screens.add result
+    result.resize(result.width, result.height)
+    result.pre_draw = proc(self: Screen) = discard
+    result.post_draw = proc(self: Screen) = discard
+    result.frame_interval = 1
+    result.display_scale = 1.0
+
+proc newTextureScreen*(engine: MyouEngine, texture: Texture,  depth_type: FramebufferDepthType = DepthRenderBuffer, depth_format = Depth_u24): Screen =
+    ## Creates a new virtual screen from a texture to render to it.
+    
+    # TODO: check that it's not a compressed texture
+    assert texture.tex_type == Tex2D, "Only 2D textures are supported"
+    return engine.newFramebufferScreen engine.newFramebuffer(
+        texture.width, texture.height,
+        format = texture.format,
+        texture = texture,
+        depth_type = depth_type,
+        depth_format = depth_format,
+    )
+
+proc setTexture*(self: Screen, texture: Texture) =
+    ## Change the texture of a render-to-texture screen.
+    
+    assert texture != nil
+    assert self.framebuffer.texture != nil
+    self.framebuffer.set_texture texture
+
 proc destroy*(self: Screen) =
     ## Destroys the screen/window and all its resources. If you destroy the main
     ## screen, the first screen created after it will become the main screen. If
@@ -117,7 +162,8 @@ proc add_viewport*(self: Screen, camera: Camera) =
 
 proc `vsync=`*(self: Screen, vsync: bool) =
     ## Change the vsync setting of the screen/window.
-    cast[Window](self.window).set_vsync vsync
+    if self.window != nil:
+        cast[Window](self.window).set_vsync vsync
 
 proc get_ray_direction*(viewport: Viewport, position: Vec2): Vec3 =
     ## Calculates a vector that points from the camera towards the given screen