render/vulkan: allow rendering to non-8-bit buffers

This is implemented by a two-subpass rendering scheme; the first
subpass draws (and blends) onto a linear R16G16B16A16_SFLOAT buffer,
while the second subpass performs linear->srgb conversion, writing
onto the actual output buffer.

2 files changed, 22 insertions, 0 deletions

diff --git a/render/vulkan/shaders/meson.build b/render/vulkan/shaders/meson.build
index 906618c2..50f4a1f0 100644
--- a/render/vulkan/shaders/meson.build
+++ b/render/vulkan/shaders/meson.build
@@ -2,6 +2,7 @@ vulkan_shaders_src = [
 	'common.vert',
 	'texture.frag',
 	'quad.frag',
+	'output.frag',
 ]
 
 vulkan_shaders = []
diff --git a/render/vulkan/shaders/output.frag b/render/vulkan/shaders/output.frag
new file mode 100644
index 00000000..28a8cdc5
--- /dev/null
+++ b/render/vulkan/shaders/output.frag
@@ -0,0 +1,21 @@
+#version 450
+
+layout (input_attachment_index = 0, binding = 0) uniform subpassInput in_color;
+
+layout(location = 0) in vec2 uv;
+layout(location = 0) out vec4 out_color;
+
+float linear_to_srgb(float x) {
+	return max(min(x * 12.92, 0.04045), 1.055 * pow(x, 1. / 2.4) - 0.055);
+}
+
+void main() {
+	vec4 val = subpassLoad(in_color).rgba;
+	out_color = vec4(
+		linear_to_srgb(val.r),
+		linear_to_srgb(val.g),
+		linear_to_srgb(val.b),
+		val.a
+	);
+}
+