vo_opengl: split out a helper for drawing primitives

Useful if we want to reduce the size of gl_video.c further.

To some degree this emulates traditional glDrawArrays() usage. It also
leaves a loophole for avoiding a reupload every time by leaving
ptr==NULL, although this is unused for now.

video/out/gl_utils.c

@@ -298,6 +298,27 @@ void gl_vao_bind_attribs(struct gl_vao *vao, GLuint program)
         gl->BindAttribLocation(program, n, vao->entries[n].name);
 }
 
+// Draw the vertex data (as described by the gl_vao_entry entries) in ptr
+// to the screen. num is the number of vertexes. prim is usually GL_TRIANGLES.
+// If ptr is NULL, then skip the upload, and use the data uploaded with the
+// previous call.
+void gl_vao_draw_data(struct gl_vao *vao, GLenum prim, void *ptr, size_t num)
+{
+    GL *gl = vao->gl;
+
+    if (ptr) {
+        gl->BindBuffer(GL_ARRAY_BUFFER, vao->buffer);
+        gl->BufferData(GL_ARRAY_BUFFER, num * vao->stride, ptr, GL_DYNAMIC_DRAW);
+        gl->BindBuffer(GL_ARRAY_BUFFER, 0);
+    }
+
+    gl_vao_bind(vao);
+
+    gl->DrawArrays(prim, 0, num);
+
+    gl_vao_unbind(vao);
+}
+
 // Create a texture and a FBO using the texture as color attachments.
 //  gl_target: GL_TEXTURE_2D
 //  gl_filter: GL_LINEAR

video/out/gl_utils.h

@@ -44,8 +44,10 @@ mp_image_t *glGetWindowScreenshot(GL *gl);
 void mp_log_source(struct mp_log *log, int lev, const char *src);
 
 struct gl_vao_entry {
+    // used for shader / glBindAttribLocation
     const char *name;
-    int num_elems;
+    // glVertexAttribPointer() arguments
+    int num_elems;      // size (number of elements)
     GLenum type;
     bool normalized;
     int offset;
@@ -53,9 +55,9 @@ struct gl_vao_entry {
 
 struct gl_vao {
     GL *gl;
-    GLuint vao;
-    GLuint buffer;
-    int stride; // always assuming interleaved elements
+    GLuint vao;     // the VAO object, or 0 if unsupported by driver
+    GLuint buffer;  // GL_ARRAY_BUFFER used for the data
+    int stride;     // size of each element (interleaved elements are assumed)
     const struct gl_vao_entry *entries;
 };
 
@@ -65,6 +67,7 @@ void gl_vao_uninit(struct gl_vao *vao);
 void gl_vao_bind(struct gl_vao *vao);
 void gl_vao_unbind(struct gl_vao *vao);
 void gl_vao_bind_attribs(struct gl_vao *vao, GLuint program);
+void gl_vao_draw_data(struct gl_vao *vao, GLenum prim, void *ptr, size_t num);
 
 struct fbotex {
     GL *gl;

video/out/gl_video.c

@@ -465,20 +465,9 @@ void gl_video_set_debug(struct gl_video *p, bool enable)
 
 static void draw_triangles(struct gl_video *p, struct vertex *vb, int vert_count)
 {
-    GL *gl = p->gl;
-
     assert(vert_count % 3 == 0);
 
-    gl->BindBuffer(GL_ARRAY_BUFFER, p->vao.buffer);
-    gl->BufferData(GL_ARRAY_BUFFER, vert_count * sizeof(struct vertex), vb,
-                   GL_DYNAMIC_DRAW);
-    gl->BindBuffer(GL_ARRAY_BUFFER, 0);
-
-    gl_vao_bind(&p->vao);
-
-    gl->DrawArrays(GL_TRIANGLES, 0, vert_count);
-
-    gl_vao_unbind(&p->vao);
+    gl_vao_draw_data(&p->vao, GL_TRIANGLES, vb, vert_count);
 
     debug_check_gl(p, "after rendering");
 }