feat: Soporte OpenGL ES 3.1 para Raspberry Pi

- Creados shaders GLSL ES 3.1 (crtpi_*_es.glsl)
- Detección automática: intenta cargar ES primero, fallback a Desktop
- Windows: pide OpenGL 3.3 Core Profile explícitamente
- Linux/RPi: deja que SDL elija (usará OpenGL ES si está disponible)
- assets.txt actualizado con shaders ES como opcionales

Resuelve problema en RPi 5 donde OpenGL 3.3 Core no está soportado
pero OpenGL ES 3.1 sí lo está mediante drivers Mesa/VideoCore.

data/shaders/crtpi_fragment_es.glsl

@@ -0,0 +1,160 @@
+#version 310 es
+
+// OpenGL ES 3.1 - Compatible con Raspberry Pi 5
+precision highp float;
+
+// Configuración
+#define SCANLINES
+#define MULTISAMPLE
+#define GAMMA
+//#define FAKE_GAMMA
+//#define CURVATURE
+//#define SHARPER
+#define MASK_TYPE 2
+
+#define CURVATURE_X 0.05
+#define CURVATURE_Y 0.1
+#define MASK_BRIGHTNESS 0.80
+#define SCANLINE_WEIGHT 6.0
+#define SCANLINE_GAP_BRIGHTNESS 0.12
+#define BLOOM_FACTOR 3.5
+#define INPUT_GAMMA 2.4
+#define OUTPUT_GAMMA 2.2
+
+// Inputs desde vertex shader
+in vec2 vTexCoord;
+in float vFilterWidth;
+#if defined(CURVATURE)
+in vec2 vScreenScale;
+#endif
+
+// Output
+out vec4 FragColor;
+
+// Uniforms
+uniform sampler2D Texture;
+uniform vec2 TextureSize;
+
+#if defined(CURVATURE)
+vec2 Distort(vec2 coord)
+{
+	vec2 CURVATURE_DISTORTION = vec2(CURVATURE_X, CURVATURE_Y);
+	vec2 barrelScale = vec2(1.0) - (0.23 * CURVATURE_DISTORTION);
+	coord *= vScreenScale;
+	coord -= vec2(0.5);
+	float rsq = coord.x * coord.x + coord.y * coord.y;
+	coord += coord * (CURVATURE_DISTORTION * rsq);
+	coord *= barrelScale;
+	if (abs(coord.x) >= 0.5 || abs(coord.y) >= 0.5)
+		coord = vec2(-1.0);
+	else
+	{
+		coord += vec2(0.5);
+		coord /= vScreenScale;
+	}
+	return coord;
+}
+#endif
+
+float CalcScanLineWeight(float dist)
+{
+	return max(1.0 - dist * dist * SCANLINE_WEIGHT, SCANLINE_GAP_BRIGHTNESS);
+}
+
+float CalcScanLine(float dy)
+{
+	float scanLineWeight = CalcScanLineWeight(dy);
+#if defined(MULTISAMPLE)
+	scanLineWeight += CalcScanLineWeight(dy - vFilterWidth);
+	scanLineWeight += CalcScanLineWeight(dy + vFilterWidth);
+	scanLineWeight *= 0.3333333;
+#endif
+	return scanLineWeight;
+}
+
+void main()
+{
+#if defined(CURVATURE)
+	vec2 texcoord = Distort(vTexCoord);
+	if (texcoord.x < 0.0) {
+		FragColor = vec4(0.0);
+		return;
+	}
+#else
+	vec2 texcoord = vTexCoord;
+#endif
+
+	vec2 texcoordInPixels = texcoord * TextureSize;
+
+#if defined(SHARPER)
+	vec2 tempCoord = floor(texcoordInPixels) + vec2(0.5);
+	vec2 coord = tempCoord / TextureSize;
+	vec2 deltas = texcoordInPixels - tempCoord;
+	float scanLineWeight = CalcScanLine(deltas.y);
+	vec2 signs = sign(deltas);
+	deltas.x *= 2.0;
+	deltas = deltas * deltas;
+	deltas.y = deltas.y * deltas.y;
+	deltas.x *= 0.5;
+	deltas.y *= 8.0;
+	deltas /= TextureSize;
+	deltas *= signs;
+	vec2 tc = coord + deltas;
+#else
+	float tempY = floor(texcoordInPixels.y) + 0.5;
+	float yCoord = tempY / TextureSize.y;
+	float dy = texcoordInPixels.y - tempY;
+	float scanLineWeight = CalcScanLine(dy);
+	float signY = sign(dy);
+	dy = dy * dy;
+	dy = dy * dy;
+	dy *= 8.0;
+	dy /= TextureSize.y;
+	dy *= signY;
+	vec2 tc = vec2(texcoord.x, yCoord + dy);
+#endif
+
+	vec3 colour = texture(Texture, tc).rgb;
+
+#if defined(SCANLINES)
+#if defined(GAMMA)
+#if defined(FAKE_GAMMA)
+	colour = colour * colour;
+#else
+	colour = pow(colour, vec3(INPUT_GAMMA));
+#endif
+#endif
+	scanLineWeight *= BLOOM_FACTOR;
+	colour *= scanLineWeight;
+
+#if defined(GAMMA)
+#if defined(FAKE_GAMMA)
+	colour = sqrt(colour);
+#else
+	colour = pow(colour, vec3(1.0 / OUTPUT_GAMMA));
+#endif
+#endif
+#endif
+
+#if MASK_TYPE == 0
+	FragColor = vec4(colour, 1.0);
+#elif MASK_TYPE == 1
+	float whichMask = fract(gl_FragCoord.x * 0.5);
+	vec3 mask;
+	if (whichMask < 0.5)
+		mask = vec3(MASK_BRIGHTNESS, 1.0, MASK_BRIGHTNESS);
+	else
+		mask = vec3(1.0, MASK_BRIGHTNESS, 1.0);
+	FragColor = vec4(colour * mask, 1.0);
+#elif MASK_TYPE == 2
+	float whichMask = fract(gl_FragCoord.x * 0.3333333);
+	vec3 mask = vec3(MASK_BRIGHTNESS, MASK_BRIGHTNESS, MASK_BRIGHTNESS);
+	if (whichMask < 0.3333333)
+		mask.x = 1.0;
+	else if (whichMask < 0.6666666)
+		mask.y = 1.0;
+	else
+		mask.z = 1.0;
+	FragColor = vec4(colour * mask, 1.0);
+#endif
+}

data/shaders/crtpi_vertex_es.glsl

@@ -0,0 +1,51 @@
+#version 310 es
+
+// OpenGL ES 3.1 - Compatible con Raspberry Pi 5
+precision highp float;
+
+// Configuración
+#define SCANLINES
+#define MULTISAMPLE
+#define GAMMA
+//#define FAKE_GAMMA
+//#define CURVATURE
+//#define SHARPER
+#define MASK_TYPE 2
+
+#define CURVATURE_X 0.05
+#define CURVATURE_Y 0.1
+#define MASK_BRIGHTNESS 0.80
+#define SCANLINE_WEIGHT 6.0
+#define SCANLINE_GAP_BRIGHTNESS 0.12
+#define BLOOM_FACTOR 3.5
+#define INPUT_GAMMA 2.4
+#define OUTPUT_GAMMA 2.2
+
+// Inputs (desde VAO)
+layout(location = 0) in vec2 aPosition;
+layout(location = 1) in vec2 aTexCoord;
+
+// Outputs al fragment shader
+out vec2 vTexCoord;
+out float vFilterWidth;
+#if defined(CURVATURE)
+out vec2 vScreenScale;
+#endif
+
+// Uniforms
+uniform vec2 TextureSize;
+
+void main()
+{
+#if defined(CURVATURE)
+	vScreenScale = vec2(1.0, 1.0);
+#endif
+	// Calcula filterWidth dinámicamente basándose en la altura de la textura
+	vFilterWidth = (768.0 / TextureSize.y) / 3.0;
+
+	// Pasar coordenadas de textura (invertir Y para SDL)
+	vTexCoord = vec2(aTexCoord.x, 1.0 - aTexCoord.y) * 1.0001;
+
+	// Posición del vértice (ya en espacio de clip [-1, 1])
+	gl_Position = vec4(aPosition, 0.0, 1.0);
+}