Add SDL3 GPU backend (Vulkan/Metal) with OpenGL fallback

shaders/_common/passthrough.vert.msl

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+#include <metal_stdlib>
+using namespace metal;
+
+// Shared fullscreen-triangle vertex shader for the SDL3 GPU backend.
+// Emits uv in Shadertoy convention: (0,0) bottom-left, (1,1) top-right.
+
+struct PassthroughVOut {
+    float4 pos [[position]];
+    float2 uv;
+};
+
+vertex PassthroughVOut passthrough_vs(uint vid [[vertex_id]]) {
+    const float2 positions[3] = { {-1.0, -1.0}, {3.0, -1.0}, {-1.0, 3.0} };
+    PassthroughVOut out;
+    float2 pos = positions[vid];
+    out.uv = pos * 0.5 + 0.5;
+    out.pos = float4(pos.x, -pos.y, 0.0, 1.0);
+    return out;
+}

shaders/_common/passthrough.vk.glsl

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+#version 450
+
+// Shared fullscreen-triangle vertex shader for the SDL3 GPU backend.
+// Emits vUV in Shadertoy convention: (0,0) bottom-left, (1,1) top-right.
+// Y flipped in NDC because Vulkan/Metal point Y down by default.
+
+layout(location = 0) out vec2 vUV;
+
+void main() {
+    const vec2 positions[3] = vec2[3](
+        vec2(-1.0, -1.0),
+        vec2( 3.0, -1.0),
+        vec2(-1.0,  3.0)
+    );
+    vec2 pos = positions[gl_VertexIndex];
+    vUV = pos * 0.5 + 0.5;
+    gl_Position = vec4(pos.x, -pos.y, 0.0, 1.0);
+}

shaders/cineshader_lava/meta.txt

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+Name: Cineshader Lava
+Author: edankwan

shaders/creation/meta.txt

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+Name: Creation by Silexars
+Author: Danguafer

shaders/cube_lines/meta.txt

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+Name: Cube lines
+Author: Danil

shaders/dbz/meta.txt

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+Name: New Leaked 3I/Atlas NASA Footage
+Author: msm01

shaders/fractal_pyramid/meta.txt

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+Name: Fractal Pyramid
+Author: bradjamesgrant

shaders/just_another_cube/meta.txt

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+Name: Just Another Cube
+Author: mrange

shaders/octograms/meta.txt

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+Name: Octograms
+Author: whisky_shusuky

shaders/remember/meta.txt

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+Name: Remember
+Author: diatribes

shaders/seascape/meta.txt

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+Name: Seascape
+Author: Alexander Alekseev

shaders/shader_art_coding_introduction/meta.txt

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+Name: Shader Art Coding Introduction
+Author: kishimisu

shaders/test/meta.txt

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+Name: Test
+Author: JailDesigner

shaders/test/test.frag.msl

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+#include <metal_stdlib>
+using namespace metal;
+
+// Test shader (Metal Shading Language port of test.vk.glsl).
+// Author: JailDesigner
+
+struct ShadertoyUBO {
+    float iTime;
+    float2 iResolution;
+};
+
+struct PassthroughVOut {
+    float4 pos [[position]];
+    float2 uv;
+};
+
+static float3 palette(float t) {
+    float3 a = float3(1.0, 0.5, 0.5);
+    float3 b = float3(1.0, 0.5, 0.5);
+    float3 c = float3(1.0, 1.0, 1.0);
+    float3 d = float3(0.263, 0.416, 0.557);
+    return a + b * cos(6.28318 * (c * t * d));
+}
+
+fragment float4 test_fs(PassthroughVOut in [[stage_in]],
+                        constant ShadertoyUBO& u [[buffer(0)]]) {
+    float2 fragCoord = in.uv * u.iResolution;
+    float2 uv = (fragCoord * 2.0 - u.iResolution) / u.iResolution.y;
+    float d = length(uv);
+    float3 col = palette(d);
+    d = sin(d * 8.0 + u.iTime) / 8.0;
+    d = abs(d);
+    d = 0.02 / d;
+    col *= d;
+    return float4(col, 1.0);
+}

shaders/test/test.vk.glsl

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+#version 450
+
+// Name: Test
+// Author: JailDesigner
+//
+// Vulkan port of test.gl.glsl. Bindings follow the SDL3 GPU convention:
+//   set=3, binding=0 — fragment uniform buffer (ShadertoyUniforms in C++).
+
+layout(location = 0) in  vec2 vUV;
+layout(location = 0) out vec4 FragColor;
+
+layout(set = 3, binding = 0) uniform ShadertoyUBO {
+    float iTime;
+    vec2  iResolution;
+} u;
+
+vec3 palette(float t) {
+    vec3 a = vec3(1.0, 0.5, 0.5);
+    vec3 b = vec3(1.0, 0.5, 0.5);
+    vec3 c = vec3(1.0, 1.0, 1.0);
+    vec3 d = vec3(0.263, 0.416, 0.557);
+    return a + b * cos(6.28318 * (c * t * d));
+}
+
+void mainImage(out vec4 fragColor, in vec2 fragCoord) {
+    vec2 uv = (fragCoord * 2.0 - u.iResolution) / u.iResolution.y;
+    float d = length(uv);
+    vec3 col = palette(d);
+    d = sin(d * 8.0 + u.iTime) / 8.0;
+    d = abs(d);
+    d = 0.02 / d;
+    col *= d;
+    fragColor = vec4(col, 1.0);
+}
+
+void main() {
+    vec2 fragCoordPixels = vUV * u.iResolution;
+    vec4 outColor;
+    mainImage(outColor, fragCoordPixels);
+    FragColor = outColor;
+}

shaders/water/meta.txt

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+Name: Water
+Author: diatribes