Initial (manual) import

TempleOSCD/Demo/Lectures/ScrnMemory.HC

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+//This just shows how scrn memory works.
+//See $LK,"::/Demo/Lectures/MiniGrLib.HC"$
+
+U0 PlotXY(I64 x,I64 y)
+{
+//Scrn bits are revd
+  LBts(text.vga_alias,y*GR_WIDTH+x^7);
+}
+
+U0 Main()
+{
+  I64 i;
+  //This makes all 4 color planes active.
+  OutU8(VGAP_IDX,VGAR_MAP_MASK);
+  OutU8(VGAP_DATA,WHITE);
+  MemSet(text.vga_alias,0,GR_WIDTH*GR_HEIGHT/8);
+
+  OutU8(VGAP_IDX,VGAR_MAP_MASK);
+  OutU8(VGAP_DATA,RED);
+  for (i=0;i<200;i++)
+    PlotXY(i,i);
+
+  OutU8(VGAP_IDX,VGAR_MAP_MASK);
+  OutU8(VGAP_DATA,GREEN);
+  for (i=0;i<200;i++)
+    PlotXY(100,i);
+
+  OutU8(VGAP_IDX,VGAR_MAP_MASK);
+  OutU8(VGAP_DATA,BLUE);
+  for (i=0;i<200;i++)
+    PlotXY(200-i,i);
+/*If you want a mixed color sel multiple planes
+but you have to be sure the unseled planes
+are zero, so sel them and make them zero.
+You can't do reads on VGA memory, by the way.
+That means no read-modify-writes, too.
+*/
+  Busy(4000000);
+
+  //TempleOS has a 4 plane memory duplicate of the scrn, $LK,"gr.scrn_image",A="MN:CGrGlbls"$,
+  //and only writes actual changes.  See $LK,"GrUpdateVGAGraphics",A="MN:GrUpdateVGAGraphics"$().
+  //<CTRL-ALT-v> will flush scrn VGA cache.
+  VGAFlush;
+}
+
+Main;
+
+//See $LK,"::/Demo/Lectures/GraphicsCPULoad.HC"$.
+