Randomise parameters from a button click

IPlugEffect.cpp

#include "IPlugEffect.h"
#include "IPlug_include_in_plug_src.h"
#include "IControls.h"

int kMsgTagRandomise = 0;

IPlugEffect::IPlugEffect(const InstanceInfo& info)
: Plugin(info, MakeConfig(kNumParams, kNumPresets))
{
  GetParam(kGain)->InitDouble("Gain", 0., 0., 100.0, 0.01, "%");

#if IPLUG_EDITOR // http://bit.ly/2S64BDd
  mMakeGraphicsFunc = [&]() {
    return MakeGraphics(*this, PLUG_WIDTH, PLUG_HEIGHT, PLUG_FPS, GetScaleForScreen(PLUG_WIDTH, PLUG_HEIGHT));
  };
  
  mLayoutFunc = [&](IGraphics* pGraphics) {
    pGraphics->AttachCornerResizer(EUIResizerMode::Scale, false);
    pGraphics->AttachPanelBackground(COLOR_GRAY);
    pGraphics->LoadFont("Roboto-Regular", ROBOTO_FN);
    const IRECT b = pGraphics->GetBounds();
    pGraphics->AttachControl(new ITextControl(b.GetMidVPadded(50), "Hello iPlug 2!", IText(50)));
    pGraphics->AttachControl(new IVKnobControl(b.GetCentredInside(100).GetVShifted(-100), kGain));
    pGraphics->AttachControl(new IVButtonControl(b.GetFromTop(100), SplashClickActionFunc, "Randomise"))->SetAnimationEndActionFunction([&](IControl* pCaller){
      
//      Note: in a non-distributed plugin, it's also OK to do this here, or inside a customised IControl's OnMouseDown()...
//      RandomiseParamValues(); // loops over all the params and sets them to a random value
//      SendCurrentParamValuesFromDelegate(); // updates the UI controls linked to parameter values
//      DirtyParametersFromUI(); // updates the host with the new parameter values
      
      // but I prefer to send a message...
      pCaller->GetDelegate()->SendArbitraryMsgFromUI(kMsgTagRandomise);
    });
  };
#endif
}

#if IPLUG_DSP
void IPlugEffect::ProcessBlock(sample** inputs, sample** outputs, int nFrames)
{
  const double gain = GetParam(kGain)->Value() / 100.;
  const int nChans = NOutChansConnected();
  
  for (int s = 0; s < nFrames; s++) {
    for (int c = 0; c < nChans; c++) {
      outputs[c][s] = inputs[c][s] * gain;
    }
  }
}
#endif

bool IPlugEffect::OnMessage(int msgTag, int ctrlTag, int dataSize, const void* pData)
{
  // and handle here...
  if (msgTag == kMsgTagRandomise) {
    RandomiseParamValues(); // loops over all the params and sets them to a random value
    SendCurrentParamValuesFromDelegate(); // updates the UI controls linked to parameter values
    DirtyParametersFromUI(); // updates the host with the new parameter values
    return true;
  }
  
  return false;
}

IPlugEffect.h

#pragma once

#include "IPlug_include_in_plug_hdr.h"

const int kNumPresets = 1;

enum EParams
{
  kGain = 0,
  kNumParams
};

using namespace iplug;
using namespace igraphics;

class IPlugEffect final : public Plugin
{
public:
  IPlugEffect(const InstanceInfo& info);

  bool OnMessage(int msgTag, int ctrlTag, int dataSize, const void* pData) override;
#if IPLUG_DSP // http://bit.ly/2S64BDd
  void ProcessBlock(sample** inputs, sample** outputs, int nFrames) override;
#endif
};