OpenGL and Vulkan examples; ptr(int)/int(ptr); trailing commas in calls; drop .fn hint

- examples/opengl.fch: OpenGL 3.3 core, shaders, VAO/VBO, a spinning triangle (checked offscreen)
- examples/vulkan.fch: instance, GPUs with properties/memory/queues, logical device and queue
- ptr(n) and int(p) conversions for C APIs that pass offsets as pointers
- .ptr works on string literals; a comma after the last call argument is allowed
- a missing header included by an imported header is now named in the error
- the old .fn extension hint is gone (Finch is new, there are no old files)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/opengl.fch

@@ -0,0 +1,105 @@
+// Modern OpenGL (3.3 core): a spinning, colorful triangle drawn with shaders.
+// Shows structs of numbers going to the GPU, C out-parameters with addr(), and
+// pointers made from numbers with ptr(...). Needs GLFW and OpenGL (in shell.nix).
+import "opengl.h"
+link "glfw"
+link "GL"
+
+fn compileShader(u32 kind, str source) -> u32 {
+    shader := glCreateShader(kind)
+    src := source.ptr
+    glShaderSource(shader, 1, addr(src), null)
+    glCompileShader(shader)
+    i32 ok
+    glGetShaderiv(shader, GL_COMPILE_STATUS, addr(ok))
+    if ok == 0 {
+        log := " ".repeat(1024)
+        glGetShaderInfoLog(shader, 1024, null, log)
+        print("shader error:", str(log.ptr))
+        exit(1)
+    }
+    return shader
+}
+
+fn makeProgram() -> u32 {
+    vertex := "#version 330 core\n" +
+        "layout(location = 0) in vec2 pos;\n" +
+        "layout(location = 1) in vec3 color;\n" +
+        "uniform float time;\n" +
+        "out vec3 vColor;\n" +
+        "void main() {\n" +
+        "    float c = cos(time), s = sin(time);\n" +
+        "    gl_Position = vec4(c * pos.x - s * pos.y, s * pos.x + c * pos.y, 0.0, 1.0);\n" +
+        "    vColor = color;\n" +
+        "}\n"
+    fragment := "#version 330 core\n" +
+        "in vec3 vColor;\n" +
+        "out vec4 outColor;\n" +
+        "void main() { outColor = vec4(vColor, 1.0); }\n"
+
+    vs := compileShader(GL_VERTEX_SHADER, vertex)
+    fs := compileShader(GL_FRAGMENT_SHADER, fragment)
+    program := glCreateProgram()
+    glAttachShader(program, vs)
+    glAttachShader(program, fs)
+    glLinkProgram(program)
+    glDeleteShader(vs)
+    glDeleteShader(fs)
+    return program
+}
+
+fn main() {
+    if glfwInit() == 0 {
+        print("could not start GLFW")
+        return
+    }
+    defer glfwTerminate()
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3)
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3)
+    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE)
+
+    window := glfwCreateWindow(800, 600, "Finch + OpenGL", null, null)
+    if window == null {
+        print("could not open a window (does your GPU support OpenGL 3.3?)")
+        return
+    }
+    glfwMakeContextCurrent(window)
+    glfwSwapInterval(1)
+    print("OpenGL", str(glGetString(GL_VERSION)), "on", str(glGetString(GL_RENDERER)))
+
+    // x, y, r, g, b for each corner
+    []f32 vertices = [
+         0.0,  0.6,   1.0, 0.48, 0.1,
+        -0.6, -0.4,   0.2, 0.6,  1.0,
+         0.6, -0.4,   0.6, 1.0,  0.4,
+    ]
+    u32 vao
+    u32 vbo
+    glGenVertexArrays(1, addr(vao))
+    glGenBuffers(1, addr(vbo))
+    glBindVertexArray(vao)
+    glBindBuffer(GL_ARRAY_BUFFER, vbo)
+    glBufferData(GL_ARRAY_BUFFER, vertices.len * 4, vertices.ptr, GL_STATIC_DRAW)
+    i32 stride = 5 * 4
+    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, stride, ptr(0))
+    glEnableVertexAttribArray(0)
+    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, stride, ptr(2 * 4))
+    glEnableVertexAttribArray(1)
+
+    program := makeProgram()
+    timeLoc := glGetUniformLocation(program, "time")
+
+    while glfwWindowShouldClose(window) == 0 {
+        glClearColor(0.106, 0.122, 0.165, 1.0)
+        glClear(GL_COLOR_BUFFER_BIT)
+        glUseProgram(program)
+        glUniform1f(timeLoc, f32(glfwGetTime()))
+        glDrawArrays(GL_TRIANGLES, 0, 3)
+        glfwSwapBuffers(window)
+        glfwPollEvents()
+    }
+
+    glDeleteBuffers(1, addr(vbo))
+    glDeleteVertexArrays(1, addr(vao))
+    glDeleteProgram(program)
+}