From 1d2f521e0bc600737e319eb26c5d7d25eee79bc7 Mon Sep 17 00:00:00 2001
From: Aaron Culliney <devnull@deadc0de.org>
Date: Sat, 24 Nov 2018 15:16:38 -0800
Subject: [PATCH] Fix graphics tearing and stuttering for disk images that sync
 to video scanner

    - Use a second framebuffer to avoid tearing
    - Occasionally stall graphics thread for ~4ms until CPU thread (video scanner) completes drawing a frame
    - These fixes seem to essentially fix graphics issues with Dagen Brock's Flappie Bird (flapple140.po.gz disk image)
---
 src/display.c       |  4 +++-
 src/video/glvideo.c | 19 +++++++++++++++++--
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/display.c b/src/display.c
index d2611784..c28fbda6 100644
--- a/src/display.c
+++ b/src/display.c
@@ -73,6 +73,7 @@ static PIXEL_TYPE *general_colors[NUM_COLOROPTS] = { 0 };
 #define FB_SIZ (SCANWIDTH*SCANHEIGHT)
 
 static PIXEL_TYPE fbFull[FB_SIZ + (SCANWIDTH<<1)] = { 0 }; // HACK NOTE: extra scanlines used for sampling
+static PIXEL_TYPE fbDone[FB_SIZ] = { 0 };
 
 // ----------------------------------------------------------------------------
 // Initialization routines
@@ -956,7 +957,7 @@ void display_flashText(void) {
 }
 
 PIXEL_TYPE *display_getCurrentFramebuffer(void) {
-    return fbFull;
+    return fbDone;
 }
 
 void display_flushScanline(scan_data_t *scandata) {
@@ -996,6 +997,7 @@ void display_frameComplete(void) {
 
     SCOPE_TRACE_CPU("frameComplete");
 
+    memcpy(/*dst:*/fbDone, /*src:*/fbFull, sizeof(fbDone));
     video_setDirty(FB_DIRTY_FLAG);
 
 #if TESTING
diff --git a/src/video/glvideo.c b/src/video/glvideo.c
index 4541d690..7fbf0fba 100644
--- a/src/video/glvideo.c
+++ b/src/video/glvideo.c
@@ -13,6 +13,7 @@
 
 #include <regex.h>
 
+// HACK NOTE : display.c "fbDone" buffer is the crtModel->texPixels to avoid a memcpy
 #define FB_PIXELS_PASS_THRU 1
 
 static int viewportX = 0;
@@ -331,11 +332,25 @@ static void glvideo_render(void) {
     glUniformMatrix4fv(uniformMVPIdx, 1, GL_FALSE, mvpIdentity);
 #endif
 
-    unsigned long wasDirty = (video_clearDirty(FB_DIRTY_FLAG) & FB_DIRTY_FLAG);
-
     glActiveTexture(TEXTURE_ACTIVE_FRAMEBUFFER);
     glBindTexture(GL_TEXTURE_2D, crtModel->textureName);
     glUniform1i(texSamplerLoc, TEXTURE_ID_FRAMEBUFFER);
+
+    unsigned long wasDirty = (video_clearDirty(FB_DIRTY_FLAG) & FB_DIRTY_FLAG);
+    if (!wasDirty) {
+        // Framebuffer is not dirty, so stall here to wait for cpu thread to (potentially) complete the video frame ...
+        // This seems to improve "stuttering" of Dagen Brock's Flappy Bird
+        SCOPE_TRACE_VIDEO("sleep");
+
+        struct timespec deltat = {
+            .tv_sec = 0,
+            .tv_nsec = NANOSECONDS_PER_SECOND / 240,
+        };
+        nanosleep(&deltat, NULL); // approx 4.714ms
+
+        wasDirty = (video_clearDirty(FB_DIRTY_FLAG) & FB_DIRTY_FLAG);
+    }
+
     if (wasDirty) {
         SCOPE_TRACE_VIDEO("glvideo texImage2D");
         _HACKAROUND_GLTEXIMAGE2D_PRE(TEXTURE_ACTIVE_FRAMEBUFFER, crtModel->textureName);