diff --git a/src/framebuffer2.h b/src/framebuffer2.h
new file mode 100644
--- /dev/null
+++ b/src/framebuffer2.h
@@ -0,0 +1,56 @@
+/*
+  Copyright © 2017 Hasan Yavuz Özderya
+
+  This file is part of serialplot.
+
+  serialplot is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  serialplot is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with serialplot.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+// IMPORTANT NOTE: this file will be renamed to "framebuffer.h" when
+// stream work is complete
+
+#ifndef FRAMEBUFFER_H
+#define FRAMEBUFFER_H
+
+struct Range
+{
+    double min, max;
+};
+
+/// Abstract base class for all frame buffers.
+class FrameBuffer
+{
+public:
+    virtual unsigned size() const = 0;
+    virtual double sample(unsigned i) const = 0;
+    virtual Range limits() const = 0;
+};
+
+/// Common base class for index and writable frame buffers
+class ResizableBuffer : public FrameBuffer
+{
+    /// Resize buffer
+    virtual void resize(unsigned n) = 0;
+};
+
+/// Abstract base class for writable frame buffers
+class WFrameBuffer : public ResizableBuffer
+{
+    /// Add samples to the buffer
+    virtual void addSamples(double* samples, unsigned n) = 0;
+    /// Reset all data to 0
+    virtual void clear() = 0;
+};
+
+#endif // FRAMEBUFFER_H
diff --git a/src/indexbuffer.cpp b/src/indexbuffer.cpp
new file mode 100644
--- /dev/null
+++ b/src/indexbuffer.cpp
@@ -0,0 +1,49 @@
+/*
+  Copyright © 2017 Hasan Yavuz Özderya
+
+  This file is part of serialplot.
+
+  serialplot is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  serialplot is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with serialplot.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <QtGlobal>
+
+#include "indexbuffer.h"
+
+IndexBuffer::IndexBuffer(unsigned n)
+{
+    _size = n;
+}
+
+unsigned IndexBuffer::size() const
+{
+    return _size;
+}
+
+void IndexBuffer::resize(unsigned n)
+{
+    _size = n;
+}
+
+double IndexBuffer::sample(unsigned i) const
+{
+    Q_ASSERT(i < _size);
+
+    return i;
+}
+
+Range IndexBuffer::limits() const
+{
+    return Range{0, _size-1.};
+}
diff --git a/src/indexbuffer.h b/src/indexbuffer.h
new file mode 100644
--- /dev/null
+++ b/src/indexbuffer.h
@@ -0,0 +1,42 @@
+/*
+  Copyright © 2017 Hasan Yavuz Özderya
+
+  This file is part of serialplot.
+
+  serialplot is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  serialplot is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with serialplot.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef INDEXBUFFER_H
+#define INDEXBUFFER_H
+
+// IMPORTANT TODO: rename to "framebuffer.h" when stream work is done.
+#include "framebuffer2.h"
+
+/// A simple frame buffer that simply returns requested index as
+/// value.
+class IndexBuffer : public ResizableBuffer
+{
+public:
+    IndexBuffer(unsigned n);
+
+    unsigned size() const;
+    double sample(unsigned i) const;
+    Range limits() const;
+    void resize(unsigned n);
+
+private:
+    unsigned _size;
+};
+
+#endif
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -27,6 +27,7 @@ add_executable(Test EXCLUDE_FROM_ALL
   ../src/samplepack.cpp
   ../src/sink.cpp
   ../src/source.cpp
+  ../src/indexbuffer.cpp
   )
 add_test(NAME test1 COMMAND Test)
 qt5_use_modules(Test Widgets)
diff --git a/tests/test.cpp b/tests/test.cpp
--- a/tests/test.cpp
+++ b/tests/test.cpp
@@ -22,6 +22,7 @@
 
 #include "samplepack.h"
 #include "source.h"
+#include "indexbuffer.h"
 
 TEST_CASE("samplepack with no X", "[memory]")
 {
@@ -180,3 +181,24 @@ TEST_CASE("source", "[memory, stream]")
     source._feed(pack);
     REQUIRE(sink.totalFed == 100);
 }
+
+TEST_CASE("IndexBuffer", "[memory, buffer]")
+{
+    IndexBuffer buf(10);
+
+    REQUIRE(buf.size() == 10);
+    for (unsigned i = 0; i < 10; i++)
+    {
+        REQUIRE(buf.sample(i) == i);
+    }
+    auto l = buf.limits();
+    REQUIRE(l.min == 0);
+    REQUIRE(l.max == 9);
+
+    buf.resize(20);
+    REQUIRE(buf.size() == 20);
+    REQUIRE(buf.sample(15) == 15);
+    l = buf.limits();
+    REQUIRE(l.min == 0);
+    REQUIRE(l.max == 19);
+}