From 99dc4bf4cedda6f8c71ce978a945b8f445d31105 Mon Sep 17 00:00:00 2001
From: Heiko Lewin <hlewin@gmx.de>
Date: Tue, 19 Jan 2021 11:26:33 +0000
Subject: [PATCH] Fix device errors for GLESv2 contexts Ignore GLerrors when
 re-selecting a (possibly deleted) GLprogram

---
 src/cairo-gl-info.c    | 42 +++++++++++++++++++++++++++++++++++++-----
 src/cairo-gl-shaders.c | 18 +++++++++++++++---
 2 files changed, 52 insertions(+), 8 deletions(-)

diff --git a/src/cairo-gl-info.c b/src/cairo-gl-info.c
index 26b7b4551..53f5b1720 100644
--- a/src/cairo-gl-info.c
+++ b/src/cairo-gl-info.c
@@ -27,6 +27,7 @@
  *
  * Contributor(s):
  *      Alexandros Frantzis <alexandros.frantzis@linaro.org>
+ *      Heiko Lewin <heiko.lewin@gmx.de>
  */
 
 #include "cairoint.h"
@@ -57,22 +58,53 @@ _cairo_gl_get_version (void)
     return CAIRO_GL_VERSION_ENCODE (major, minor);
 }
 
+
+cairo_gl_flavor_t
+_cairo_gl_degrade_flavor_by_build_features (cairo_gl_flavor_t flavor) {
+    switch(flavor) {
+    case CAIRO_GL_FLAVOR_DESKTOP:
+#if CAIRO_HAS_GL_SURFACE
+	return CAIRO_GL_FLAVOR_DESKTOP;
+#else
+	return CAIRO_GL_FLAVOR_NONE;
+#endif
+
+    case CAIRO_GL_FLAVOR_ES3:
+#if CAIRO_HAS_GLESV3_SURFACE
+	return CAIRO_GL_FLAVOR_ES3;
+#else
+	/* intentional fall through: degrade to GLESv2 if GLESv3-surfaces are not available */
+#endif
+
+    case CAIRO_GL_FLAVOR_ES2:
+#if CAIRO_HAS_GLESV2_SURFACE
+	return CAIRO_GL_FLAVOR_ES2;
+#else
+	/* intentional fall through: no OpenGL in first place or no surfaces for it's version */
+#endif
+
+    default:
+	return CAIRO_GL_FLAVOR_NONE;
+    }
+}
+
 cairo_gl_flavor_t
 _cairo_gl_get_flavor (void)
 {
     const char *version = (const char *) glGetString (GL_VERSION);
     cairo_gl_flavor_t flavor;
 
-    if (version == NULL)
+    if (version == NULL) {
 	flavor = CAIRO_GL_FLAVOR_NONE;
-    else if (strstr (version, "OpenGL ES 3") != NULL)
+    } else if (strstr (version, "OpenGL ES 3") != NULL) {
 	flavor = CAIRO_GL_FLAVOR_ES3;
-    else if (strstr (version, "OpenGL ES 2") != NULL)
+    } else if (strstr (version, "OpenGL ES 2") != NULL) {
 	flavor = CAIRO_GL_FLAVOR_ES2;
-    else
+    } else {
 	flavor = CAIRO_GL_FLAVOR_DESKTOP;
+    }
 
-    return flavor;
+    return _cairo_gl_degrade_flavor_by_build_features(flavor);
 }
 
 unsigned long
diff --git a/src/cairo-gl-shaders.c b/src/cairo-gl-shaders.c
index f789ae1d9..745302f87 100644
--- a/src/cairo-gl-shaders.c
+++ b/src/cairo-gl-shaders.c
@@ -37,6 +37,7 @@
  *	Eric Anholt <eric@anholt.net>
  *	T. Zachary Laine <whatwasthataddress@gmail.com>
  *	Alexandros Frantzis <alexandros.frantzis@linaro.org>
+ *  H. Lewin <heiko.lewin@gmx.de>
  */
 
 #include "cairoint.h"
@@ -900,7 +901,7 @@ _cairo_gl_shader_compile_and_link (cairo_gl_context_t *ctx,
  * texture unit 1 if present, so we can just initialize these once at
  * compile time.
  */
-static void
+static cairo_status_t
 _cairo_gl_shader_set_samplers (cairo_gl_context_t *ctx,
 			       cairo_gl_shader_t *shader)
 {
@@ -924,8 +925,14 @@ _cairo_gl_shader_set_samplers (cairo_gl_context_t *ctx,
     if (location != -1) {
 	dispatch->Uniform1i (location, CAIRO_GL_TEX_MASK);
     }
-
+    if(_cairo_gl_get_error()) return CAIRO_STATUS_DEVICE_ERROR;
     dispatch->UseProgram (saved_program);
+    /* Pop and ignore a possible gl-error when restoring the previous program.
+     * It may be that being selected in the gl-context was the last reference
+     * to the shader.
+     */
+    _cairo_gl_get_error(); 
+    return CAIRO_STATUS_SUCCESS;
 }
 
 void
@@ -1084,7 +1091,12 @@ _cairo_gl_get_shader_by_type (cairo_gl_context_t *ctx,
 	return status;
     }
 
-    _cairo_gl_shader_set_samplers (ctx, &entry->shader);
+    status = _cairo_gl_shader_set_samplers (ctx, &entry->shader);
+    if (unlikely (status)) {
+	_cairo_gl_shader_fini (ctx, &entry->shader);
+	free (entry);
+	return status;
+    }
 
     status = _cairo_cache_insert (&ctx->shaders, &entry->base);
     if (unlikely (status)) {