Added gameboy-advance preset

Created a preset for the gameboy shader optimized for Game Boy Advance games. This preset creates a cool LCD effect where pixels really pop.

handheld/gameboy-advance.slangp

@@ -0,0 +1,49 @@
+shaders = 5
+
+shader0 = shaders/gameboy/shader-files/gb-pass0.slang
+filter_linear0 = false
+scale_type0 = viewport
+scale0 = 1.0
+alias0 = "PASS0"
+color_toggle = "1.000000"
+baseline_alpha = "1.000000"
+response_time = "0.000000"
+contrast = "1.000000"
+screen_light = "0.850000"
+
+shader1 = shaders/gameboy/shader-files/gb-pass1.slang
+filter_linear1 = false
+scale_type1 = source
+scale1 = 1.0
+alias1 = "PASS1"
+
+shader2 = shaders/gameboy/shader-files/gb-pass2.slang
+filter_linear2 = false
+scale_type2 = source
+scale2 = 1.0
+alias2 = "PASS2"
+
+shader3 = shaders/gameboy/shader-files/gb-pass3.slang
+filter_linear3 = false
+scale_type3 = source
+scale3 = 1.0
+alias3 = "PASS3"
+
+shader4 = shaders/gameboy/shader-files/gb-pass4.slang
+filter_linear4 = false
+scale_type4 = source
+scale4 = 1.0
+alias4 = "PASS4"
+
+shader4 = shaders/gameboy/shader-files/gb-pass5.slang
+filter_linear4 = false
+scale_type4 = source
+scale4 = 1.0
+alias4 = "PASS5"
+
+
+textures = COLOR_PALETTE;BACKGROUND
+COLOR_PALETTE = shaders/gameboy/resources/sample-palettes/b-w-palette.png
+COLOR_PALETTE_linear = false
+BACKGROUND = shaders/gameboy/resources/sample-bgs/paper-bg.png
+BACKGROUND_linear = true