From 53b8dabe7322d61e03a4b7f9710c79664493e31a Mon Sep 17 00:00:00 2001
From: Mike Walters <mike@flomp.net>
Date: Thu, 25 Jun 2015 00:04:27 +0100
Subject: [PATCH] Cache current view for reuse on next paint

---
 inputsource.cpp | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 inputsource.h   |  5 +++++
 2 files changed, 52 insertions(+)

diff --git a/inputsource.cpp b/inputsource.cpp
index d68c2e0..826e45b 100644
--- a/inputsource.cpp
+++ b/inputsource.cpp
@@ -45,6 +45,48 @@ InputSource::~InputSource() {
 }
 
 void InputSource::GetViewport(float *dest, int x, int y, int width, int height, int zoom) {
+    int crossover_start_lines = 0;
+    int crossover_end_lines = 0;
+    if (m_output_cache != nullptr && m_cache_valid) {
+        // Scroll down, with at least some of previous cache still in view
+        if (m_prev_y <= y && y < m_prev_y + m_prev_height) {
+            float *crossover_start = m_output_cache + (y - m_prev_y) * m_fft_size;
+            int crossover_lines;
+            // This covers the case of a window size reduction
+            if (y + height < m_prev_y + m_prev_height) {
+                crossover_lines = (m_prev_y + height - y);
+            } else {
+                crossover_lines = (m_prev_y + m_prev_height - y);
+            }
+            int crossover_length = crossover_lines * m_fft_size * sizeof(float);
+            memcpy(dest, crossover_start, crossover_length);
+
+            crossover_start_lines = crossover_lines;
+        // Scroll up
+        } else if (y <= m_prev_y && m_prev_y < y + height) {
+            float *crossover_start = dest + (m_prev_y - y) * m_fft_size;
+            int crossover_lines = y + height - m_prev_y;
+            int crossover_length = crossover_lines * m_fft_size * sizeof(float);
+            memcpy(crossover_start, m_output_cache, crossover_length);
+
+            crossover_end_lines = crossover_lines;
+        }
+    }
+
+    if (m_output_cache == nullptr || height != m_prev_height) {
+        m_output_cache = (float*)realloc(m_output_cache, m_fft_size * height * sizeof(float));
+    }
+
+    m_prev_y = y;
+    m_prev_height = height;
+
+    float *cache_ptr = m_output_cache;
+    y += crossover_start_lines;
+    height -= crossover_start_lines;
+    height -= crossover_end_lines;
+    dest += crossover_start_lines * m_fft_size;
+    cache_ptr += crossover_start_lines * m_fft_size;
+
     fftwf_complex *sample_ptr = &m_data[y * GetFFTStride()];
 
     for (int i = 0; i < height; i++) {
@@ -66,9 +108,12 @@ void InputSource::GetViewport(float *dest, int x, int y, int width, int height,
             float magdb = 10 * log2(mag) / log2(10);
             *dest = magdb;
             dest++;
+            *cache_ptr = magdb;
+            cache_ptr++;
         }
         sample_ptr += GetFFTStride();
     }
+    m_cache_valid = true;
 }
 
 int InputSource::GetHeight() {
@@ -87,6 +132,7 @@ bool InputSource::ZoomIn() {
         m_zoom = m_max_zoom;
         return false;
     }
+    m_cache_valid = false;
     return true;
 }
 
@@ -96,6 +142,7 @@ bool InputSource::ZoomOut() {
         m_zoom = 0;
         return false;
     }
+    m_cache_valid = false;
     return true;
 }
 
diff --git a/inputsource.h b/inputsource.h
index 3986c2f..86e052e 100644
--- a/inputsource.h
+++ b/inputsource.h
@@ -10,6 +10,11 @@ private:
     fftwf_complex *m_data;
     int m_fft_size;
 
+    float *m_output_cache = nullptr;
+    bool m_cache_valid = false;
+    int m_prev_y = -1;
+    int m_prev_height = -1;
+
     fftwf_complex *m_fftw_in;
     fftwf_complex *m_fftw_out;
     fftwf_plan m_fftw_plan;