How to read pixels from a rendered texture?

[stefs]

I want to read the RGB values from specific texels in a textured polygon, where the texture is a rendered texture attached to a render node. For “normal” textures this works fine by reading from the data array obtained with the texture’s getImageData method.
However, for a texture created with viz.addRenderTexture and attached to the render node using attachTexture, there is no reference to any data returned.

I then tried to attach a texture created with viz.addBlankTexture to the render node. To my surprise this will render correctly to the texture which becomes visible on the rendered polygon. Also a valid reference to a data array is returned with getImageData. But this buffer is empty.

Any suggestions how to access the pixel buffer of a rendered texture?

[farshizzo]

There is no built-in support for this in Vizard 3. It is possible in Vizard 4 though. In case you decide to upgrade, here is how to get access to the raw image data of a render texture in Vizard 4:

imgData = texture.saveToBuffer('<raw>')

[stefs]

Ok, this seems to work for RGBA textures in Vizard 4.0
But there are other issues now. I try to read the depth values also. First issue is that .getPixelSize() returns zero (also for RGBA textures). By trial and error I found that if the texture is viz.TEX_DEPTH, at least one byte /character is returned per depth value. All other depth formats TEX_DEPTH_16, TEX_DEPTH_24, TEX_DEPTH_32 will cause an "error pixelFormat = 81a5". Please try the script below.
Any ideas how I can get at least 16 bit depth values are greatly appreciated.
(I could work around it by having a specific render pass with a shader that renders Z as RGBA into the color buffer)

import viz

global render_texture_RGBA 
global render_texture_Depth 
	
def set_render_node_view(render_node):
	render_node.setBuffer(viz.RENDER_FBO)
	render_node.setInheritView(False)
	render_node.setMatrix(viz.Transform())
	render_node.setPosition(-3.0,0.0,0)
	render_node.setEuler([90,0,0])
	render_node.setProjectionMatrix(viz.MainWindow.getProjectionMatrix())
	
def setup_render_node_RGBA():
	global render_texture_RGBA 
	render_texture_RGBA = viz.addRenderTexture([512, 512], type = viz.TEX_2D, format = viz.TEX_RGBA)
	render_node_RGBA = viz.addRenderNode()
	render_node_RGBA.setRenderTexture(render_texture_RGBA, buffer = viz.RENDER_COLOR)
	render_node_RGBA.setBuffer(viz.RENDER_FBO)
	set_render_node_view(render_node_RGBA)

def setup_render_node_Depth(depth_format):
	global render_texture_Depth 
	render_texture_Depth = viz.addRenderTexture([512, 512], type = viz.TEX_2D, format = depth_format)
	render_node_Depth = viz.addRenderNode()
	render_node_Depth.setRenderTexture(render_texture_Depth, buffer = viz.AUTO_COMPUTE)
	render_node_Depth.setBuffer(viz.RENDER_FBO)
	set_render_node_view(render_node_Depth)

def pick_texel_RGBA(texture, pos = [0.5, 0.5]):
	size = texture.getSize() 
	bpt  = texture.getPixelSize() # getPixelSize always returns 0
	bpt = 4                       # set to 4 as we know format is RGBA
	data = texture.saveToBuffer('<raw>')
	if (data == None):
		return None
	else:
		ix = int(float(size[0]) * pos[0])
		iy = int(float(size[1]) * pos[1])
		idx = (iy * size[1] + ix ) * bpt
		sample = []
		for i in range(bpt):
			sample.append(ord(data[idx+i]))
		return sample

def pick_texel_Depth(texture, pos = [0.5, 0.5]):
	size = texture.getSize() 
	bpt  = texture.getPixelSize() # getPixelSize always returns 0
	bpt = 1                       # set to 1 as this sees to work for format Depth
	data = texture.saveToBuffer('<raw>')
	if (data == None):
		return None
	else:
		ix = int(float(size[0]) * pos[0])
		iy = int(float(size[1]) * pos[1])
		idx = (iy * size[1] + ix ) * bpt
		sample = []
		for i in range(bpt):
			sample.append(ord(data[idx+i]))
		return sample
	
def onKeyDown(key):
	global render_texture_RGBA 
	if key == 'p':
		print 'RGBA/Depth of texel at [0.5, 0.5] is : ',pick_texel_RGBA(render_texture_RGBA,[0.5, 0.5]), pick_texel_Depth(render_texture_Depth,[0.5, 0.5])   
		print 'RGBA/Depth of texel at [0.55, 0.5] is : ',pick_texel_RGBA(render_texture_RGBA,[0.55,0.5]), pick_texel_Depth(render_texture_Depth,[0.55, 0.5])  
		print 'RGBA/Depth of texel at [0.6, 0.5] is : ',pick_texel_RGBA(render_texture_RGBA,[0.6,0.5]), pick_texel_Depth(render_texture_Depth,[0.6, 0.5])  
	
viz.add('ball.wrl')
viz.MainView.setPosition(0.0,0.0,-3)

setup_render_node_RGBA()
setup_render_node_Depth(viz.TEX_DEPTH)    # only format that works, will give 8-bit limited depth buffer
#setup_render_node_Depth(viz.TEX_DEPTH_16) # will cause an "error pixelFormat = 81a5" error at texture.saveToBuffer()
#setup_render_node_Depth(viz.TEX_DEPTH_24) # will cause an "error pixelFormat = 81a5" error at texture.saveToBuffer()
#setup_render_node_Depth(viz.TEX_DEPTH_32) # will cause an "error pixelFormat = 81a5" error at texture.saveToBuffer()

tex_quad = viz.addTexQuad()
tex_quad.texture(render_texture_RGBA)
#tex_quad.texture(render_texture_Depth) # show depth buffer, instead
tex_quad.setPosition(1.0,0.0,0)
tex_quad.setScale(viz.MainWindow.getAspectRatio(),1,1)
viz.callback(viz.KEYDOWN_EVENT,onKeyDown)
viz.go()