adds LinRamp node

src/nodes.jl

@@ -178,3 +178,33 @@ end
 typealias AudioInput AudioNode{InputRenderer}
 AudioInput(channel::Int) = AudioInput(InputRenderer(channel))
 export AudioInput
+
+#### Ramp ####
+
+type LinRampRenderer <: AudioRenderer
+    start::AudioSample
+    finish::AudioSample
+    dur::Float32
+end
+
+typealias LinRamp AudioNode{LinRampRenderer}
+function LinRamp(start::Real, finish::Real, dur::Real)
+    LinRamp(LinRampRenderer(start, finish, dur))
+end
+export LinRamp
+
+
+function render(node::LinRampRenderer, device_input::AudioBuf, info::DeviceInfo)
+    ramp_samples = int(node.dur * info.sample_rate)
+    block_samples = min(ramp_samples, info.buf_size)
+    out_block = Array(AudioSample, block_samples)
+    for i in 1:block_samples
+        out_block[i] = node.start + ((i-1) / ramp_samples) *
+                (node.finish - node.start)
+    end
+    node.dur -= block_samples / info.sample_rate
+    node.start += block_samples / ramp_samples * (node.finish - node.start)
+
+    return out_block
+end
+

test/test_nodes.jl

@@ -91,3 +91,15 @@ info("Testing Gain...")
 gained = TestNode() * 0.75
 render_output = render(gained, dev_input, test_info)
 @test render_output == 0.75 * AudioSample[1:test_info.buf_size]
+
+info("Testing LinRamp...")
+ramp = LinRamp(0.25, 0.80, 1)
+expected = convert(AudioBuf, linspace(0.25, 0.80, test_info.sample_rate+1))
+render_output = render(ramp, dev_input, test_info)
+@test render_output == expected[1:test_info.buf_size]
+# TODO: there seems to be some slight error in the 2nd block. I THINK it's just
+# floating point stuff, but we should probably check to be sure
+#render_output = render(ramp, dev_input, test_info)
+#println("expected: $(expected[test_info.buf_size+1:test_info.buf_size+10])")
+#println("output: $(render_output[1:10])")
+#@test render_output == expected[(test_info.buf_size+1):(2*test_info.buf_size)]