render/vulkan: add Vulkan renderer

This new renderer is implemented with the existing wlr_renderer API
(which is known to be sub-optimal for some operations). It's not
used by default, but users can opt-in by setting WLR_RENDERER=vulkan.

The renderer depends on VK_EXT_image_drm_format_modifier and
VK_EXT_physical_device_drm.

Co-authored-by: Simon Ser <contact@emersion.fr>
Co-authored-by: Jan Beich <jbeich@FreeBSD.org>

render/vulkan/shaders/common.vert

@@ -0,0 +1,25 @@
+#version 450
+
+// we use a mat4 since it uses the same size as mat3 due to
+// alignment. Easier to deal with (tighly-packed) mat4 though.
+layout(push_constant, row_major) uniform UBO {
+	mat4 proj;
+	vec2 uv_offset;
+	vec2 uv_size;
+} data;
+
+layout(location = 0) out vec2 uv;
+
+// 4 outlining points and uv coords
+const vec2[] values = {
+	{0, 0},
+	{1, 0},
+	{1, 1},
+	{0, 1},
+};
+
+void main() {
+	vec2 pos = values[gl_VertexIndex % 4];
+	uv = data.uv_offset + pos * data.uv_size;
+	gl_Position = data.proj * vec4(pos, 0.0, 1.0);
+}

render/vulkan/shaders/meson.build

@@ -0,0 +1,20 @@
+vulkan_shaders_src = [
+	'common.vert',
+	'texture.frag',
+	'quad.frag',
+]
+
+vulkan_shaders = []
+foreach shader : vulkan_shaders_src
+	name = shader.underscorify() + '_data'
+	args = [glslang, '-V', '@INPUT@', '-o', '@OUTPUT@', '--vn', name]
+	header = custom_target(
+		shader + '_spv',
+		output: shader + '.h',
+		input: shader,
+		command: args)
+
+	vulkan_shaders += [header]
+endforeach
+
+wlr_files += vulkan_shaders

render/vulkan/shaders/quad.frag

@@ -0,0 +1,10 @@
+#version 450
+
+layout(location = 0) out vec4 out_color;
+layout(push_constant) uniform UBO {
+	layout(offset = 80) vec4 color;
+} data;
+
+void main() {
+	out_color = data.color;
+}

render/vulkan/shaders/texture.frag

@@ -0,0 +1,25 @@
+#version 450
+
+layout(set = 0, binding = 0) uniform sampler2D tex;
+
+layout(location = 0) in vec2 uv;
+layout(location = 0) out vec4 out_color;
+
+layout(push_constant) uniform UBO {
+	layout(offset = 80) float alpha;
+} data;
+
+void main() {
+	out_color = textureLod(tex, uv, 0);
+
+	// We expect this shader to output pre-alpha-multiplied color values.
+	// alpha < 0.0 means that this shader should ignore the texture's alpha
+	// value.
+	if (data.alpha < 0.0) {
+		out_color.a = -data.alpha;
+		out_color.rgb *= -data.alpha;
+	} else {
+		out_color *= data.alpha;
+	}
+}
+