Bugfix - alpha was not working when using pre-render textures, as I was

not correctly clearing/configuring alpha blending.

fsl/fsleyes/gl/lightboxcanvas.py

@@ -19,6 +19,7 @@ import OpenGL.GL as gl
 import fsl.fsleyes.displaycontext.canvasopts as canvasopts
 import fsl.fsleyes.gl.slicecanvas            as slicecanvas
 import fsl.fsleyes.gl.resources              as glresources
+import fsl.fsleyes.gl.routines               as glroutines
 import fsl.fsleyes.gl.textures               as textures
 
 
@@ -723,8 +724,6 @@ class LightBoxCanvas(slicecanvas.SliceCanvas):
         if not self._setGLContext():
             return
 
-        gl.glClearColor(*self.bgColour)
-
         if self.renderMode == 'offscreen':
             
             log.debug('Rendering to off-screen texture')
@@ -740,10 +739,12 @@ class LightBoxCanvas(slicecanvas.SliceCanvas):
             
             rt.bindAsRenderTarget()
             rt.setRenderViewport(self.xax, self.yax, lo, hi)
-            gl.glClear(gl.GL_COLOR_BUFFER_BIT)
+            glroutines.clear((0, 0, 0, 0)) 
             
         else:
             self._setViewport()
+            glroutines.clear(self.bgColour) 
+
 
         startSlice = self.ncols * self.topRow
         endSlice   = startSlice + self.nrows * self.ncols
@@ -795,6 +796,7 @@ class LightBoxCanvas(slicecanvas.SliceCanvas):
             rt.unbindAsRenderTarget()
             rt.restoreViewport()
             self._setViewport()
+            glroutines.clear(self.bgColour)
             rt.drawOnBounds(
                 0,
                 self.displayBounds.xlo,

fsl/fsleyes/gl/routines.py

@@ -20,6 +20,22 @@ import fsl.utils.transform as transform
 log = logging.getLogger(__name__)
 
 
+def clear(bgColour):
+    """Clears the current frame buffer, and does some standard setup
+    operations.
+    """
+
+    # set the background colour
+    gl.glClearColor(*bgColour)
+
+    # clear the buffer
+    gl.glClear(gl.GL_COLOR_BUFFER_BIT | gl.GL_DEPTH_BUFFER_BIT)
+
+    # enable transparency
+    gl.glEnable(gl.GL_BLEND) 
+    gl.glBlendFunc(gl.GL_SRC_ALPHA, gl.GL_ONE_MINUS_SRC_ALPHA)
+
+
 def show2D(xax, yax, width, height, lo, hi):
     """Configures the OpenGL viewport for 2D othorgraphic display.
 

fsl/fsleyes/gl/slicecanvas.py

@@ -12,8 +12,7 @@ functionality to display a 2D slice from a collection of 3D overlays.
 import copy
 import logging
 
-import numpy     as np 
-import OpenGL.GL as gl
+import numpy as np 
 
 import props
 
@@ -904,13 +903,6 @@ class SliceCanvas(props.HasProperties):
             size = self._getSize()
             
         width, height = size
-
-        # clear the canvas
-        gl.glClear(gl.GL_COLOR_BUFFER_BIT | gl.GL_DEPTH_BUFFER_BIT)
-
-        # enable transparency
-        gl.glEnable(gl.GL_BLEND)
-        gl.glBlendFunc(gl.GL_SRC_ALPHA, gl.GL_ONE_MINUS_SRC_ALPHA)        
         
         if (len(self.overlayList) == 0) or \
            (width  == 0)                or \
@@ -1017,8 +1009,6 @@ class SliceCanvas(props.HasProperties):
         if width == 0 or height == 0:
             return
 
-        gl.glClearColor(*self.bgColour)
-
         if not self._setGLContext():
             return
 
@@ -1026,7 +1016,8 @@ class SliceCanvas(props.HasProperties):
         # display bounds and canvas size
         if self.renderMode is not 'offscreen':
             self._setViewport()
-
+            glroutines.clear(self.bgColour)
+            
         for overlay in self.displayCtx.getOrderedOverlays():
 
             display = self.displayCtx.getDisplay(overlay)
@@ -1075,7 +1066,7 @@ class SliceCanvas(props.HasProperties):
                 rt.bindAsRenderTarget()
                 rt.setRenderViewport(self.xax, self.yax, lo, hi)
                 
-                gl.glClear(gl.GL_COLOR_BUFFER_BIT)
+                glroutines.clear((0, 0, 0, 0))
 
                 globj.preDraw()
                 globj.draw(self.pos.z)
@@ -1106,6 +1097,7 @@ class SliceCanvas(props.HasProperties):
         # to the screen canvas.
         if self.renderMode == 'offscreen':
             self._setViewport()
+            glroutines.clear(self.bgColour)
             self._drawOffscreenTextures() 
 
         if self.showCursor:

fsl/fsleyes/gl/textures/rendertexturestack.py

@@ -249,10 +249,10 @@ class RenderTextureStack(object):
         oldProjMat    = gl.glGetFloatv(  gl.GL_PROJECTION_MATRIX)
         oldMVMat      = gl.glGetFloatv(  gl.GL_MODELVIEW_MATRIX)
 
+        tex.bindAsRenderTarget()
         glroutines.show2D(xax, yax, width, height, lo, hi)
+        glroutines.clear((0, 0, 0, 0))
 
-        tex.bindAsRenderTarget()
-        gl.glClear(gl.GL_COLOR_BUFFER_BIT)
         self.__globj.preDraw()
         self.__globj.draw(zpos)
         self.__globj.postDraw()