feat(renderer): add CRT shader filter with configurable effects

Add CRT (Cathode Ray Tube) shader implementation as scaling filter
options (CRT EasyMode and CRT Royale) in the Window Adapting Filter
dropdown. Provides classic TV effects including scanlines, phosphor
masks, curvature distortion, gamma correction, bloom, brightness, and
alpha transparency.

- Add CRTEasyMode and CRTRoyale to ScalingFilter enum
- Implement vulkan_crt_easymode.frag shader with single-pass effects
- Integrate CRT filter into WindowAdaptPass rendering pipeline
- Add configurable CRT parameters to settings with user-friendly labels
- Add UI translations for desktop and Android platforms
- Support CRT push constants in present pipeline

The CRT filter appears alongside other scaling filters like FSR and
FSR 2.0. CRT parameter settings are only active when a CRT filter
is selected.

Signed-off-by: Zephyron <zephyron@citron-emu.org>

src/video_core/host_shaders/CMakeLists.txt

@@ -1,5 +1,5 @@
 # SPDX-FileCopyrightText: 2018 yuzu Emulator Project
-# SPDX-FileCopyrightText: Copyright 2025 citron Emulator Project
+# SPDX-FileCopyrightText: 2026 citron Emulator Project
 # SPDX-License-Identifier: GPL-2.0-or-later
 
 set(FIDELITYFX_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/externals/FidelityFX-FSR/ffx-fsr)
@@ -74,6 +74,7 @@ set(SHADER_FILES
     vulkan_present_scaleforce_fp32.frag
     vulkan_present_scalefx_fp16.frag
     vulkan_present_scalefx_fp32.frag
+    vulkan_crt_easymode.frag
     vulkan_quad_indexed.comp
     vulkan_taa.frag
     vulkan_taa.vert

src/video_core/host_shaders/vulkan_crt_easymode.frag

@@ -0,0 +1,133 @@
+// SPDX-FileCopyrightText: Copyright 2026 citron Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+//
+// CRT EasyMode shader - Single-pass CRT effects
+// Based on Libretro's crt-easymode shader
+// https://github.com/libretro/common-shaders/blob/master/crt/shaders/crt-easymode.cg
+
+#version 460 core
+
+layout(location = 0) in vec2 frag_tex_coord;
+layout(location = 0) out vec4 color;
+
+layout(binding = 0) uniform sampler2D color_texture;
+
+layout(push_constant) uniform CRTPushConstants {
+    layout(offset = 132) float scanline_strength;
+    layout(offset = 136) float curvature;
+    layout(offset = 140) float gamma;
+    layout(offset = 144) float bloom;
+    layout(offset = 148) int mask_type;
+    layout(offset = 152) float brightness;
+    layout(offset = 156) float alpha;
+    layout(offset = 160) float screen_width;
+    layout(offset = 164) float screen_height;
+} crt_params;
+
+const float PI = 3.141592653589793;
+
+// Apply barrel distortion (curvature)
+vec2 applyCurvature(vec2 coord) {
+    if (crt_params.curvature <= 0.0) {
+        return coord;
+    }
+
+    vec2 centered = coord - 0.5;
+    float dist = length(centered);
+    float distortion = 1.0 + crt_params.curvature * dist * dist;
+    vec2 curved = centered * distortion + 0.5;
+
+    // Clamp to valid texture coordinates
+    return clamp(curved, vec2(0.0), vec2(1.0));
+}
+
+// Generate scanlines
+float scanline(float y) {
+    if (crt_params.scanline_strength <= 0.0) {
+        return 1.0;
+    }
+
+    float scanline_pos = y * crt_params.screen_height;
+    float scanline_factor = abs(sin(scanline_pos * PI));
+
+    // Make scanlines more subtle
+    return 1.0 - crt_params.scanline_strength * scanline_factor * 0.5;
+}
+
+// Apply phosphor mask (aperture grille or shadow mask)
+vec3 applyMask(vec2 coord) {
+    if (crt_params.mask_type == 0) {
+        return vec3(1.0); // No mask
+    }
+
+    vec2 screen_pos = coord * vec2(crt_params.screen_width, crt_params.screen_height);
+
+    if (crt_params.mask_type == 1) {
+        // Aperture grille (vertical RGB stripes)
+        float mask = sin(screen_pos.x * PI * 3.0) * 0.5 + 0.5;
+        return vec3(
+            1.0 - mask * 0.2,
+            1.0 - mask * 0.15,
+            1.0 - mask * 0.2
+        );
+    } else if (crt_params.mask_type == 2) {
+        // Shadow mask (triangular pattern)
+        float x = screen_pos.x * 3.0;
+        float y = screen_pos.y * 3.0;
+        float mask = sin(x * PI) * sin(y * PI) * 0.5 + 0.5;
+        return vec3(1.0 - mask * 0.15);
+    }
+
+    return vec3(1.0);
+}
+
+// Simple bloom effect (multi-tap blur approximation)
+vec3 applyBloom(vec2 coord, vec3 original) {
+    if (crt_params.bloom <= 0.0) {
+        return original;
+    }
+
+    vec2 texel_size = 1.0 / vec2(crt_params.screen_width, crt_params.screen_height);
+    vec3 bloom_color = original;
+
+    // Simple 5-tap horizontal blur
+    for (int i = -2; i <= 2; i++) {
+        vec2 offset = vec2(float(i) * texel_size.x, 0.0);
+        vec3 sample_color = texture(color_texture, clamp(coord + offset, vec2(0.0), vec2(1.0))).rgb;
+        bloom_color += sample_color;
+    }
+
+    bloom_color /= 6.0; // Average of 5 taps + original
+
+    // Mix original with bloom
+    return mix(original, bloom_color, crt_params.bloom * 0.3);
+}
+
+void main() {
+    // Apply curvature distortion first
+    vec2 curved_coord = applyCurvature(frag_tex_coord);
+
+    // Sample the texture
+    vec3 rgb = texture(color_texture, curved_coord).rgb;
+
+    // Apply bloom
+    rgb = applyBloom(curved_coord, rgb);
+
+    // Apply phosphor mask
+    rgb *= applyMask(curved_coord);
+
+    // Apply scanlines
+    float scan = scanline(curved_coord.y);
+    rgb *= scan;
+
+    // Gamma correction
+    if (crt_params.gamma > 0.0 && crt_params.gamma != 1.0) {
+        rgb = pow(clamp(rgb, vec3(0.0), vec3(1.0)), vec3(1.0 / crt_params.gamma));
+    }
+
+    // Apply brightness adjustment
+    rgb *= crt_params.brightness;
+
+    // Clamp to valid range and apply alpha
+    color = vec4(clamp(rgb, vec3(0.0), vec3(1.0)), crt_params.alpha);
+}