Add a new renderer API

Goals:

- Extensibility: we need to be able to add new params to the calls
  to render a texture/rect. For instance we'll need to add fences to
  the render texture operation for explicit sync purposes.
- No implicit state: no more bind_buffer, begin, end.
- No matrices: these hurt Pixman and we don't need them.
- Clip regions for optimized damage repainting.

Closes: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3188

include/wlr/render/interface.h

@@ -48,6 +48,8 @@ struct wlr_renderer_impl {
 	uint32_t (*get_render_buffer_caps)(struct wlr_renderer *renderer);
 	struct wlr_texture *(*texture_from_buffer)(struct wlr_renderer *renderer,
 		struct wlr_buffer *buffer);
+	struct wlr_render_pass *(*begin_buffer_pass)(struct wlr_renderer *renderer,
+		struct wlr_buffer *buffer);
 };
 
 void wlr_renderer_init(struct wlr_renderer *renderer,
@@ -62,4 +64,19 @@ struct wlr_texture_impl {
 void wlr_texture_init(struct wlr_texture *texture, struct wlr_renderer *rendener,
 	const struct wlr_texture_impl *impl, uint32_t width, uint32_t height);
 
+struct wlr_render_pass {
+	const struct wlr_render_pass_impl *impl;
+};
+
+void wlr_render_pass_init(struct wlr_render_pass *pass,
+	const struct wlr_render_pass_impl *impl);
+
+struct wlr_render_pass_impl {
+	bool (*submit)(struct wlr_render_pass *pass);
+	void (*add_texture)(struct wlr_render_pass *pass,
+		const struct wlr_render_texture_options *options);
+	void (*add_rect)(struct wlr_render_pass *pass,
+		const struct wlr_render_rect_options *options);
+};
+
 #endif

include/wlr/render/wlr_renderer.h

@@ -12,6 +12,7 @@
 #include <stdint.h>
 #include <wayland-server-core.h>
 #include <wlr/render/wlr_texture.h>
+#include <wlr/util/box.h>
 
 struct wlr_backend;
 struct wlr_renderer_impl;
@@ -155,4 +156,71 @@ int wlr_renderer_get_drm_fd(struct wlr_renderer *r);
  */
 void wlr_renderer_destroy(struct wlr_renderer *renderer);
 
+/**
+ * A render pass accumulates drawing operations until submitted to the GPU.
+ */
+struct wlr_render_pass;
+
+/**
+ * Begin a new render pass with the supplied destination buffer.
+ *
+ * Callers must call wlr_render_pass_submit() once they are done with the
+ * render pass.
+ */
+struct wlr_render_pass *wlr_renderer_begin_buffer_pass(
+	struct wlr_renderer *renderer, struct wlr_buffer *buffer);
+
+/**
+ * Submit the render pass.
+ *
+ * The render pass cannot be used after this function is called.
+ */
+bool wlr_render_pass_submit(struct wlr_render_pass *render_pass);
+
+struct wlr_render_texture_options {
+	/* Source texture */
+	struct wlr_texture *texture;
+	/* Source coordinates, leave empty to render the whole texture */
+	struct wlr_fbox src_box;
+	/* Destination coordinates, width/height default to the texture size */
+	struct wlr_box dst_box;
+	/* Opacity between 0 (transparent) and 1 (opaque), leave NULL for opaque */
+	const float *alpha;
+	/* Clip region, leave NULL to disable clipping */
+	const pixman_region32_t *clip;
+	/* Transform applied to the source texture */
+	enum wl_output_transform transform;
+};
+
+/**
+ * Render a texture.
+ */
+void wlr_render_pass_add_texture(struct wlr_render_pass *render_pass,
+	const struct wlr_render_texture_options *options);
+
+/**
+ * A color value.
+ *
+ * Each channel has values between 0 and 1 inclusive. The R, G, B
+ * channels need to be pre-multiplied by A.
+ */
+struct wlr_render_color {
+	float r, g, b, a;
+};
+
+struct wlr_render_rect_options {
+	/* Rectangle coordinates */
+	struct wlr_box box;
+	/* Source color */
+	struct wlr_render_color color;
+	/* Clip region, leave NULL to disable clipping */
+	const pixman_region32_t *clip;
+};
+
+/**
+ * Render a rectangle.
+ */
+void wlr_render_pass_add_rect(struct wlr_render_pass *render_pass,
+	const struct wlr_render_rect_options *options);
+
 #endif

render/meson.build

@@ -8,6 +8,7 @@ endif
 wlr_files += files(
 	'dmabuf.c',
 	'drm_format_set.c',
+	'pass.c',
 	'pixel_format.c',
 	'swapchain.c',
 	'wlr_renderer.c',

render/pass.c

@@ -0,0 +1,25 @@
+#include <assert.h>
+#include <string.h>
+#include <wlr/render/interface.h>
+#include <wlr/render/wlr_renderer.h>
+
+void wlr_render_pass_init(struct wlr_render_pass *render_pass,
+		const struct wlr_render_pass_impl *impl) {
+	assert(impl->submit && impl->add_texture && impl->add_rect);
+	memset(render_pass, 0, sizeof(*render_pass));
+	render_pass->impl = impl;
+}
+
+bool wlr_render_pass_submit(struct wlr_render_pass *render_pass) {
+	return render_pass->impl->submit(render_pass);
+}
+
+void wlr_render_pass_add_texture(struct wlr_render_pass *render_pass,
+		const struct wlr_render_texture_options *options) {
+	render_pass->impl->add_texture(render_pass, options);
+}
+
+void wlr_render_pass_add_rect(struct wlr_render_pass *render_pass,
+		const struct wlr_render_rect_options *options) {
+	render_pass->impl->add_rect(render_pass, options);
+}

render/wlr_renderer.c

@@ -33,11 +33,13 @@
 
 void wlr_renderer_init(struct wlr_renderer *renderer,
 		const struct wlr_renderer_impl *impl) {
-	assert(impl->begin);
-	assert(impl->clear);
-	assert(impl->scissor);
-	assert(impl->render_subtexture_with_matrix);
-	assert(impl->render_quad_with_matrix);
+	if (!impl->begin_buffer_pass) {
+		assert(impl->begin);
+		assert(impl->clear);
+		assert(impl->scissor);
+		assert(impl->render_subtexture_with_matrix);
+		assert(impl->render_quad_with_matrix);
+	}
 	assert(impl->get_shm_texture_formats);
 	assert(impl->get_render_buffer_caps);
 
@@ -409,3 +411,11 @@ int wlr_renderer_get_drm_fd(struct wlr_renderer *r) {
 	}
 	return r->impl->get_drm_fd(r);
 }
+
+struct wlr_render_pass *wlr_renderer_begin_buffer_pass(
+		struct wlr_renderer *renderer, struct wlr_buffer *buffer) {
+	if (!renderer->impl->begin_buffer_pass) {
+		return NULL;
+	}
+	return renderer->impl->begin_buffer_pass(renderer, buffer);
+}