GUI: prepare for colors in the per-chan osc

src/gui/gradient.cpp

@@ -0,0 +1,70 @@
+/**
+ * Furnace Tracker - multi-system chiptune tracker
+ * Copyright (C) 2021-2022 tildearrow and contributors
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "gui.h"
+#include "imgui.h"
+#include <math.h>
+
+void Gradient2D::render() {
+  ImU32* g=grad.get();
+  ImU32 bgColorU=ImGui::ColorConvertFloat4ToU32(bgColor);
+
+  // 1. fill with background color
+  for (size_t i=0; i<width*height; i++) {
+    g[i]=bgColorU;
+  }
+
+  // 2. insert points
+  for (Gradient2DPoint& i: points) {
+    float pDistSquared=i.distance*i.distance;
+    printf("shading this point %f %f\n",i.x,i.y);
+    for (size_t j=0; j<height; j++) {
+      float jFloat=(float)j/(float)height;
+      float distY=jFloat-i.y;
+      for (size_t k=0; k<width; k++) {
+        float kFloat=(float)k/(float)width;
+        float distX=kFloat-i.x;
+        float distSquared=(distX*distX)+(distY*distY);
+
+        if (distSquared>=pDistSquared) continue;
+
+        float dist=(1.0-(sqrt(distSquared)/i.distance))-i.spread;
+        if (dist<0) dist=0;
+        if (dist>1) dist=1;
+
+        ImU32 shadeColor=ImGui::ColorConvertFloat4ToU32(
+          ImVec4(
+            i.color.x*i.color.w*dist,
+            i.color.y*i.color.w*dist,
+            i.color.z*i.color.w*dist,
+            1.0f
+          )
+        );
+
+        ImU32 origColor=g[j*width+k];
+        g[j*width+k]=(
+          (MIN(  0xff,    (origColor&0xff)  +  (shadeColor&0xff)  )) | // R
+          (MIN( 0xff00,  (origColor&0xff00) + (shadeColor&0xff00) )) | // G
+          (MIN(0xff0000,(origColor&0xff0000)+(shadeColor&0xff0000))) | // B
+          (origColor&0xff000000)                                       // A
+        );
+      }
+    }
+  }
+}