Add boing example

examples/screensavers/boing/boing.ino

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+// "Boing" ball example for PicoDVI library, If just starting out,
+// see the 8bit_double_buffer which explains the PicoDVI groundwork.
+// Comments in THIS file are mostly distinct & new concepts.
+// Adapted from PyPortal example in Adafruit_ILI9341 library.
+
+#include <PicoDVI.h>
+#include "graphics.h" // Graphics data
+
+// 4:3 aspect for that Amiga flavour:
+DVIGFX8 display(DVI_RES_320x240p60, true, adafruit_feather_dvi_cfg);
+
+#define YBOTTOM   123  // Ball Y coord at bottom
+#define YBOUNCE  -3.5  // Upward velocity on ball bounce
+
+// Ball coordinates are stored floating-point because screen refresh
+// is so quick, whole-pixel movements are just too fast!
+float ballx     = 20.0, bally     = YBOTTOM, // Current ball position
+      ballvx    =  0.8, ballvy    = YBOUNCE, // Ball velocity
+      ballframe = 3;                         // Ball animation frame #
+int   balloldx  = ballx, balloldy = bally;   // Prior ball position
+
+void setup() {
+  if (!display.begin()) { // Blink LED if insufficient RAM
+    pinMode(LED_BUILTIN, OUTPUT);
+    for (;;) digitalWrite(LED_BUILTIN, (millis() / 500) & 1);
+  }
+
+  // Set up color palette
+  display.setColor(0, 0xAD75); // #0 = Background color
+  display.setColor(1, 0xA815); // #1 = Grid color
+  display.setColor(2, 0x5285); // #2 = Background in shadow
+  display.setColor(3, 0x600C); // #3 = Grid in shadow
+
+  // Draw initial framebuffer contents (grid, no shadow):
+  display.drawBitmap(0, 0, (uint8_t *)background, 320, 240, 1, 0);
+  display.swap(true, true); // Duplicate same bg & palette into both buffers
+}
+
+void loop() {
+  balloldx = (int16_t)ballx; // Save prior position
+  balloldy = (int16_t)bally;
+  ballx   += ballvx;         // Update position
+  bally   += ballvy;
+  ballvy  += 0.06;           // Update Y velocity
+  if((ballx <= 15) || (ballx >= display.width() - BALLWIDTH))
+    ballvx *= -1;            // Left/right bounce
+  if(bally >= YBOTTOM) {     // Hit ground?
+    bally  = YBOTTOM;        // Clip and
+    ballvy = YBOUNCE;        // bounce up
+  }
+
+  // Determine screen area to update.  This is the bounds of the ball's
+  // prior and current positions, so the old ball is fully erased and new
+  // ball is fully drawn.
+  int16_t minx, miny, maxx, maxy, width, height;
+  // Determine bounds of prior and new positions
+  minx = ballx;
+  if(balloldx < minx)                    minx = balloldx;
+  miny = bally;
+  if(balloldy < miny)                    miny = balloldy;
+  maxx = ballx + BALLWIDTH  - 1;
+  if((balloldx + BALLWIDTH  - 1) > maxx) maxx = balloldx + BALLWIDTH  - 1;
+  maxy = bally + BALLHEIGHT - 1;
+  if((balloldy + BALLHEIGHT - 1) > maxy) maxy = balloldy + BALLHEIGHT - 1;
+
+  width  = maxx - minx + 1;
+  height = maxy - miny + 1;
+
+  // Ball animation frame # is incremented opposite the ball's X velocity
+  ballframe -= ballvx * 0.5;
+  if(ballframe < 0)        ballframe += 14; // Constrain from 0 to 13
+  else if(ballframe >= 14) ballframe -= 14;
+
+  // Set 7 palette entries to white, 7 to red, based on frame number.
+  // This makes the ball spin.
+  for(uint8_t i=0; i<14; i++) {
+    display.setColor(i + 4, ((((int)ballframe + i) % 14) < 7) ? 0xFFFF : 0xF800);
+  }
+
+  // Only the changed rectangle is drawn into the 'renderbuf' array...
+  uint8_t  c, *destPtr;
+  int16_t  bx  = minx - (int)ballx, // X relative to ball bitmap (can be negative)
+           by  = miny - (int)bally, // Y relative to ball bitmap (can be negative)
+           bgx = minx,              // X relative to background bitmap (>= 0)
+           bgy = miny,              // Y relative to background bitmap (>= 0)
+           x, y, bx1, bgx1;         // Loop counters and working vars
+  uint8_t  p;                       // 'packed' value of 2 ball pixels
+  int8_t bufIdx = 0;
+
+  uint8_t *buf = display.getBuffer(); // -> back buffer
+
+  for(y=0; y<height; y++) { // For each row...
+    destPtr = &buf[display.width() * (miny + y) + minx];
+    bx1  = bx;  // Need to keep the original bx and bgx values,
+    bgx1 = bgx; // so copies of them are made here (and changed in loop below)
+    for(x=0; x<width; x++) {
+      if((bx1 >= 0) && (bx1 < BALLWIDTH) &&  // Is current pixel row/column
+         (by  >= 0) && (by  < BALLHEIGHT)) { // inside the ball bitmap area?
+        // Yes, do ball compositing math...
+        p = ball[by][bx1 / 2];                // Get packed value (2 pixels)
+        c = (bx1 & 1) ? (p & 0xF) : (p >> 4); // Unpack high or low nybble
+        if(c == 0) { // Outside ball - just draw grid
+          c = background[bgy][bgx1 / 8] & (0x80 >> (bgx1 & 7)) ? 1 : 0;
+        } else if(c > 1) { // In ball area...
+          c += 2; // Convert to color index >= 4
+        } else { // In shadow area, draw shaded grid...
+          c = background[bgy][bgx1 / 8] & (0x80 >> (bgx1 & 7)) ? 3 : 2;
+        }
+      } else { // Outside ball bitmap, just draw background bitmap...
+        c = background[bgy][bgx1 / 8] & (0x80 >> (bgx1 & 7)) ? 1 : 0;
+      }
+      *destPtr++ = c; // Store pixel color
+      bx1++;  // Increment bitmap position counters (X axis)
+      bgx1++;
+    }
+    by++; // Increment bitmap position counters (Y axis)
+    bgy++;
+  }
+
+  display.swap(true, false); // Show & copy current background buffer to next
+}