step

examples/shaders/shapes_textures/glsl330/base.vs

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+#version 330
+
+// Input vertex attributes
+in vec3 vertexPosition;
+in vec2 vertexTexCoord;
+in vec3 vertexNormal;
+in vec4 vertexColor;
+
+// Input uniform values
+uniform mat4 mvp;
+
+// Output vertex attributes (to fragment shader)
+out vec2 fragTexCoord;
+out vec4 fragColor;
+
+// NOTE: Add here your custom variables 
+
+void main()
+{
+    // Send vertex attributes to fragment shader
+    fragTexCoord = vertexTexCoord;
+    fragColor = vertexColor;
+    
+    // Calculate final vertex position
+    gl_Position = mvp*vec4(vertexPosition, 1.0);
+}

examples/shaders/shapes_textures/glsl330/grayscale.fs

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+#version 330
+
+// Input vertex attributes (from vertex shader)
+in vec2 fragTexCoord;
+in vec4 fragColor;
+
+// Input uniform values
+uniform sampler2D texture0;
+uniform vec4 colDiffuse;
+
+// Output fragment color
+out vec4 finalColor;
+
+// NOTE: Add here your custom variables
+
+void main()
+{
+    // Texel color fetching from texture sampler
+    vec4 texelColor = texture(texture0, fragTexCoord)*colDiffuse*fragColor;
+    
+    // Convert texel color to grayscale using NTSC conversion weights
+    float gray = dot(texelColor.rgb, vec3(0.299, 0.587, 0.114));
+    
+    // Calculate final fragment color
+    finalColor = vec4(gray, gray, gray, texelColor.a);
+}

examples/shaders/shapes_textures/main.go

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+package main
+
+import (
+	"github.com/gen2brain/raylib-go/raylib"
+)
+
+func main() {
+	screenWidth := int32(800)
+	screenHeight := int32(450)
+
+	rl.InitWindow(screenWidth, screenHeight, "raylib [shaders] example - shapes and texture shaders")
+
+	fudesumi := rl.LoadTexture("fudesumi.png")
+
+	// NOTE: Using GLSL 330 shader version, on OpenGL ES 2.0 use GLSL 100 shader version
+	shader := rl.LoadShader("glsl330/base.vs", "glsl330/grayscale.fs")
+
+	rl.SetTargetFPS(60)
+
+	for !rl.WindowShouldClose() {
+		rl.BeginDrawing()
+
+		rl.ClearBackground(rl.RayWhite)
+
+		// Start drawing with default shader
+
+		rl.DrawText("USING DEFAULT SHADER", 20, 40, 10, rl.Red)
+
+		rl.DrawCircle(80, 120, 35, rl.DarkBlue)
+		rl.DrawCircleGradient(80, 220, 60, rl.Green, rl.SkyBlue)
+		rl.DrawCircleLines(80, 340, 80, rl.DarkBlue)
+
+		// Activate our custom shader to be applied on next shapes/textures drawings
+		rl.BeginShaderMode(shader)
+
+		rl.DrawText("USING CUSTOM SHADER", 190, 40, 10, rl.Red)
+
+		rl.DrawRectangle(250-60, 90, 120, 60, rl.Red)
+		rl.DrawRectangleGradientH(250-90, 170, 180, 130, rl.Maroon, rl.Gold)
+		rl.DrawRectangleLines(250-40, 320, 80, 60, rl.Orange)
+
+		// Activate our default shader for next drawings
+		rl.EndShaderMode()
+
+		rl.DrawText("USING DEFAULT SHADER", 370, 40, 10, rl.Red)
+
+		rl.DrawTriangle(rl.NewVector2(430, 80),
+			rl.NewVector2(430-60, 150),
+			rl.NewVector2(430+60, 150), rl.Violet)
+
+		rl.DrawTriangleLines(rl.NewVector2(430, 160),
+			rl.NewVector2(430-20, 230),
+			rl.NewVector2(430+20, 230), rl.DarkBlue)
+
+		rl.DrawPoly(rl.NewVector2(430, 320), 6, 80, 0, rl.Brown)
+
+		// Activate our custom shader to be applied on next shapes/textures drawings
+		rl.BeginShaderMode(shader)
+
+		rl.DrawTexture(fudesumi, 500, -30, rl.White) // Using custom shader
+
+		// Activate our default shader for next drawings
+		rl.EndShaderMode()
+
+		rl.DrawText("(c) Fudesumi sprite by Eiden Marsal", 380, screenHeight-20, 10, rl.Gray)
+
+		rl.EndDrawing()
+	}
+
+	rl.UnloadShader(shader)    // Unload shader
+	rl.UnloadTexture(fudesumi) // Unload texture
+
+	rl.CloseWindow() // Close window and OpenGL context
+}