opengl: uniforms

src/main.zig

@@ -70,6 +70,8 @@ pub fn main() !void {
         c.glClear(c.GL_COLOR_BUFFER_BIT);
 
         try program.use();
+        try program.setUniform("vertexColor", @Vector(4, f32){ 0.0, 1.0, 0.0, 1.0 });
+
         try vao.bind();
         c.glDrawArrays(c.GL_TRIANGLES, 0, 3);
 
@@ -95,8 +97,10 @@ const fs_source =
     \\#version 330 core
     \\out vec4 FragColor;
     \\
+    \\uniform vec4 vertexColor;
+    \\
     \\void main()
     \\{
-    \\    FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);
+    \\    FragColor = vertexColor;
     \\}
 ;

src/opengl/Program.zig

@@ -45,6 +45,22 @@ pub inline fn use(p: Program) !void {
     c.glUseProgram(p.id);
 }
 
+/// Requires the program is currently in use.
+pub inline fn setUniform(p: Program, n: [:0]const u8, value: anytype) !void {
+    const loc = c.glGetUniformLocation(p.id, n);
+    if (loc < 0) {
+        return error.UniformNameInvalid;
+    }
+    try errors.getError();
+
+    // Perform the correct call depending on the type of the value.
+    switch (@TypeOf(value)) {
+        @Vector(4, f32) => c.glUniform4f(loc, value[0], value[1], value[2], value[3]),
+        else => unreachable,
+    }
+    try errors.getError();
+}
+
 /// getInfoLog returns the info log for this program. This attempts to
 /// keep the log fully stack allocated and is therefore limited to a max
 /// amount of elements.