render/gles2: save/restore context when creating/submitting a render pass

This is useful for e.g. lazily blitting a texture for readback
purposes while rendering.

include/render/gles2.h

@@ -15,6 +15,8 @@
 #include <wlr/util/addon.h>
 #include <wlr/util/log.h>
 
+#include "render/egl.h"
+
 // mesa ships old GL headers that don't include this type, so for distros that use headers from
 // mesa we need to def it ourselves until they update.
 // https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23144
@@ -132,6 +134,7 @@ struct wlr_gles2_render_pass {
 	struct wlr_render_pass base;
 	struct wlr_gles2_buffer *buffer;
 	float projection_matrix[9];
+	struct wlr_egl_context prev_ctx;
 	struct wlr_gles2_render_timer *timer;
 };
 
@@ -164,6 +167,6 @@ void push_gles2_debug_(struct wlr_gles2_renderer *renderer,
 void pop_gles2_debug(struct wlr_gles2_renderer *renderer);
 
 struct wlr_gles2_render_pass *begin_gles2_buffer_pass(struct wlr_gles2_buffer *buffer,
-	struct wlr_gles2_render_timer *timer);
+	struct wlr_egl_context *prev_ctx, struct wlr_gles2_render_timer *timer);
 
 #endif

include/wlr/render/gles2.h

@@ -21,6 +21,10 @@ struct wlr_egl;
  * the current EGL is global state. The GLES2 renderer operations will save
  * and restore any previous EGL context when called. A render pass is seen as
  * a single operation.
+ *
+ * The GLES2 renderer doesn't support arbitrarily nested render passes. It
+ * supports a subset only: after a nested render pass is created, any parent
+ * render pass can't be used before the nested render pass is submitted.
  */
 
 struct wlr_renderer *wlr_gles2_renderer_create_with_drm_fd(int drm_fd);

render/gles2/pass.c

@@ -41,6 +41,7 @@ static bool render_pass_submit(struct wlr_render_pass *wlr_pass) {
 	glBindFramebuffer(GL_FRAMEBUFFER, 0);
 
 	pop_gles2_debug(renderer);
+	wlr_egl_restore_context(&pass->prev_ctx);
 
 	wlr_buffer_unlock(pass->buffer->buffer);
 	free(pass);
@@ -247,7 +248,7 @@ static const char *reset_status_str(GLenum status) {
 }
 
 struct wlr_gles2_render_pass *begin_gles2_buffer_pass(struct wlr_gles2_buffer *buffer,
-		struct wlr_gles2_render_timer *timer) {
+		struct wlr_egl_context *prev_ctx, struct wlr_gles2_render_timer *timer) {
 	struct wlr_gles2_renderer *renderer = buffer->renderer;
 	struct wlr_buffer *wlr_buffer = buffer->buffer;
 
@@ -274,6 +275,7 @@ struct wlr_gles2_render_pass *begin_gles2_buffer_pass(struct wlr_gles2_buffer *b
 	wlr_buffer_lock(wlr_buffer);
 	pass->buffer = buffer;
 	pass->timer = timer;
+	pass->prev_ctx = *prev_ctx;
 
 	matrix_projection(pass->projection_matrix, wlr_buffer->width, wlr_buffer->height,
 		WL_OUTPUT_TRANSFORM_FLIPPED_180);

render/gles2/renderer.c

@@ -433,6 +433,9 @@ static void gles2_destroy(struct wlr_renderer *wlr_renderer) {
 static struct wlr_render_pass *gles2_begin_buffer_pass(struct wlr_renderer *wlr_renderer,
 		struct wlr_buffer *wlr_buffer, const struct wlr_buffer_pass_options *options) {
 	struct wlr_gles2_renderer *renderer = gles2_get_renderer(wlr_renderer);
+
+	struct wlr_egl_context prev_ctx = {0};
+	wlr_egl_save_context(&prev_ctx);
 	if (!wlr_egl_make_current(renderer->egl)) {
 		return NULL;
 	}
@@ -448,7 +451,7 @@ static struct wlr_render_pass *gles2_begin_buffer_pass(struct wlr_renderer *wlr_
 		return NULL;
 	}
 
-	struct wlr_gles2_render_pass *pass = begin_gles2_buffer_pass(buffer, timer);
+	struct wlr_gles2_render_pass *pass = begin_gles2_buffer_pass(buffer, &prev_ctx, timer);
 	if (!pass) {
 		return NULL;
 	}