optimize renderSamples

only render sample which has changed

src/engine/engine.cpp

@@ -396,13 +396,13 @@ int DivEngine::loadSampleROMs() {
   return error;
 }
 
-void DivEngine::renderSamplesP() {
+void DivEngine::renderSamplesP(int whichSample) {
   BUSY_BEGIN;
-  renderSamples();
+  renderSamples(whichSample);
   BUSY_END;
 }
 
-void DivEngine::renderSamples() {
+void DivEngine::renderSamples(int whichSample) {
   sPreview.sample=-1;
   sPreview.pos=0;
   sPreview.dir=false;
@@ -418,8 +418,12 @@ void DivEngine::renderSamples() {
   }
 
   // step 1: render samples
-  for (int i=0; i<song.sampleLen; i++) {
-    song.sample[i]->render(formatMask);
+  if (whichSample==-1) {
+    for (int i=0; i<song.sampleLen; i++) {
+      song.sample[i]->render(formatMask);
+    }
+  } else if (whichSample>=0 && whichSample<song.sampleLen) {
+    song.sample[whichSample]->render(formatMask);
   }
 
   // step 2: render samples to dispatch

src/engine/engine.h

@@ -1064,10 +1064,14 @@ class DivEngine {
     unsigned int getSampleFormatMask();
 
     // UNSAFE render samples - only execute when locked
-    void renderSamples();
+    void renderSamples(int whichSample=-1);
 
     // public render samples
-    void renderSamplesP();
+    // values for whichSample
+    // -2: don't render anything - just update chip sample memory
+    // -1: render all samples
+    // >=0: render specific sample
+    void renderSamplesP(int whichSample=-1);
 
     // public swap channels
     void swapChannelsP(int src, int dest);