[OpenGL] Draw in 2d after drawing in 3d

BrknPhoenix

What I'm wondering, is let's say the 3d scene is drawn. Is there a way to then draw in 2d flat on the screen? For example, if I wanted to have a HUD or mouse cursor over the scene, could I just draw those straight to the screen flat?

I know I could figure out all the business as to where those things would be in 3d space and constantly move them with the camera, but it'd be a lot easier if there was just a way to draw it 2d after the 3d was done

Kitty Cat

After drawing the 3d scene, simply reset the modelview and projection matrix, then set an ortho mode (glOrtho).

1glMatrixMode(GL_PROJECTION);
2glLoadIdentity();
3gluPerspective(45.0f, float(SCREEN_W)/SCREEN_H, 1.0f, 10000.0f);
4glMatrixMode(GL_MODELVIEW);
5 
6while(playing)
7{
8    glLoadIdentity();
9    draw_3d_stuff_here();
10 
11    glMatrixMode(GL_PROJECTION);
12    glPushMatrix();
13    glLoadIdentity();
14    glOrtho(0, SCREEN_W, SCREEN_H, 0, -1, 1);
15    glMatrixMode(GL_MODELVIEW);
16 
17    draw_2d_stuff_here();
18 
19    glMatrixMode(GL_PROJECTION);
20    glPopMatrix();
21    glMatrixMode(GL_MODELVIEW);
22}

BrknPhoenix

It doesn't appear to be working. My mouse cursor, which worked in 2D, has stopped showing up when 3D was added. I put in the code that you suggested and nothing happened differently.

Kitty Cat

Show the code. Can't tell what's wrong without seeing what you're doing.

BrknPhoenix

Initial setup

    else if (projection_type == FRUSTUM)
    {
        glMatrixMode(GL_PROJECTION);
        glEnable(GL_TEXTURE_2D);
        glEnable(GL_DEPTH_TEST);        
        glLoadIdentity();
       gluPerspective(45.0f, (GLfloat)SCREEN_WIDTH / (GLfloat)SCREEN_HEIGHT, 1.0f, 1000.0f);         
        glViewport(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);           
        glClearColor(0.0f, 0.0f, 0.0f, 0.0f);        
    }
}

This is the drawing function:

void objGfx::DoDraw(int s)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);            
    
    Do3D(s);
    
    Do2D(s);    
    
    allegro_gl_flip();
}

3D function

void objGfx::Do3D(int s)
{
    switch (s)
    {
        case SCENE_TITLE:
            glMatrixMode(GL_MODELVIEW);
            glLoadIdentity();                                                                                      
            break;
        case SCENE_NONE:
            glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
        default:
            break;            
    }    
}

2D Function

1void objGfx::Do2D(int s)
2{
  glMatrixMode(GL_PROJECTION);
  glPushMatrix();
  glLoadIdentity();
  glOrtho(0, SCREEN_WIDTH, SCREEN_HEIGHT, 0, -1, 1);
  glMatrixMode(GL_MODELVIEW);
  
  switch (s)
  {
      case SCENE_TITLE:
          break;
      case SCENE_NONE:
      default:
          break;
  }
  
  if (Mouse->Visible())
  {
      Draw->Sprite(Mouse->TextureSprite(), Mouse->TextureMask(),
                   Mouse->X(), Mouse->Y(),
                   Mouse->X() + Mouse->CursorWidth(),
                   Mouse->Y() + Mouse->CursorHeight());
  }
  
  if (DEBUG)
  {
      Debug->Output();
  }
  
  glMatrixMode(GL_PROJECTION);
  glPopMatrix();
  glMatrixMode(GL_MODELVIEW);    
34}

Kitty Cat

What are the Mouse and Draw objects? At a glance, everything you pasted looks alright, so the problem is somewhere else.

BrknPhoenix

edit: I figured out the problem actually does have to do with how the mouse is being drawn, but I don't know what. I've since moved on to an attempt at a different solution.

Draw->Sprite

1void objDraw::Sprite(GLuint sprite, GLuint mask, int x1, int y1, int x2, int y2)
2{
  glEnable(GL_TEXTURE_2D);
  glEnable(GL_BLEND);
  glBlendFunc(GL_DST_COLOR, GL_ZERO);
  
  glBindTexture(GL_TEXTURE_2D, mask);
  
  glBegin(GL_QUADS);
      glTexCoord3f(0, 0, 0); glVertex3f(x1, y2, 0);
      glTexCoord3f(1, 0, 0); glVertex3f(x2, y2, 0);
      glTexCoord3f(1, 1, 0); glVertex3f(x2, y1, 0);
      glTexCoord3f(0, 1, 0); glVertex3f(x1, y1, 0);
  glEnd();
15 
  glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
  
  glBindTexture(GL_TEXTURE_2D, sprite);
  glBlendFunc(GL_ONE, GL_ONE);
  
  glBegin(GL_QUADS);
      glTexCoord3f(0, 0, 0); glVertex3f(x1, y2, 0);
      glTexCoord3f(1, 0, 0); glVertex3f(x2, y2, 0);
      glTexCoord3f(1, 1, 0); glVertex3f(x2, y1, 0);
      glTexCoord3f(0, 1, 0); glVertex3f(x1, y1, 0);        
  glEnd();
27}

Mouse everything

1#include <allegro.h>
2#include <alleggl.h>
3 
4#include "mouse.h"
5 
6#include "defines.h"
7#include "globals.h"
8 
9objMouse::objMouse()
10{
11    visible = false;
12}
13 
14objMouse::~objMouse()
15{
16    destroy_bitmap(m_sprite);
17    destroy_bitmap(m_mask);
18}
19 
20int objMouse::X()
21{
22    return mouse_x;
23}
24 
25int objMouse::Y()
26{
27    return mouse_y;
28}
29 
30int objMouse::Z()
31{
32    return mouse_z;
33}
34 
35int objMouse::LeftButton()
36{
37    if (mouse_b & 1)
38    {
39        return true;
40    }
41    else
42    {
43        return false;
44    }
45}
46 
47int objMouse::RightButton()
48{
49    if (mouse_b & 2)
50    {
51        return true;
52    }
53    else
54    {
55        return false;
56    }
57}
58 
59int objMouse::MiddleButton()
60{
61    if (mouse_b & 4)
62    {
63        return true;
64    }
65    else 
66    {
67        return false;
68    }
69}
70 
71BITMAP* objMouse::CursorSprite()
72{
73    return m_sprite;
74}
75 
76BITMAP* objMouse::CursorMask()
77{
78    return m_mask;
79}
80 
81bool objMouse::Visible()
82{
83    return visible;
84}
85 
86int objMouse::CursorWidth()
87{
88    return m_sprite->w;
89}
90 
91int objMouse::CursorHeight()
92{
93    return m_sprite->h;
94}
95 
96GLuint objMouse::TextureSprite()
97{
98    return texSprite;
99}
100 
101GLuint objMouse::TextureMask()
102{
103    return texMask;
104}
105 
106void objMouse::SetCursorSprite(const char* filename)
107{
108    m_sprite = load_bitmap(filename, NULL);
109    texSprite = allegro_gl_make_texture(m_sprite);    
110}
111 
112void objMouse::SetCursorMask(const char* filename)
113{
114    m_mask = load_bitmap(filename, NULL);
115    texMask = allegro_gl_make_texture(m_mask);
116}
117 
118void objMouse::Show()
119{
120    visible = true;
121}
122 
123void objMouse::Scare()
124{
125    visible = false;
126}
127 
128void objMouse::Draw()
129{
130    allegro_gl_set_allegro_mode();
131 
132    draw_sprite(screen, m_sprite, mouse_x, mouse_y);
133    
134    allegro_gl_unset_allegro_mode();
135}

Note the Mouse->Draw function isn't actually used... I just forgot to take it out, hehe

Thread #586476. Printed from Allegro.cc

1	glMatrixMode(GL_PROJECTION);
2	glLoadIdentity();
3	gluPerspective(45.0f, float(SCREEN_W)/SCREEN_H, 1.0f, 10000.0f);
4	glMatrixMode(GL_MODELVIEW);
5
6	while(playing)
7	{
8	glLoadIdentity();
9	draw_3d_stuff_here();
10
11	glMatrixMode(GL_PROJECTION);
12	glPushMatrix();
13	glLoadIdentity();
14	glOrtho(0, SCREEN_W, SCREEN_H, 0, -1, 1);
15	glMatrixMode(GL_MODELVIEW);
16
17	draw_2d_stuff_here();
18
19	glMatrixMode(GL_PROJECTION);
20	glPopMatrix();
21	glMatrixMode(GL_MODELVIEW);
22	}

1	void objGfx::Do2D(int s)
2	{
3	glMatrixMode(GL_PROJECTION);
4	glPushMatrix();
5	glLoadIdentity();
6	glOrtho(0, SCREEN_WIDTH, SCREEN_HEIGHT, 0, -1, 1);
7	glMatrixMode(GL_MODELVIEW);
8
9	switch (s)
10	{
11	case SCENE_TITLE:
12	break;
13	case SCENE_NONE:
14	default:
15	break;
16	}
17
18	if (Mouse->Visible())
19	{
20	Draw->Sprite(Mouse->TextureSprite(), Mouse->TextureMask(),
21	Mouse->X(), Mouse->Y(),
22	Mouse->X() + Mouse->CursorWidth(),
23	Mouse->Y() + Mouse->CursorHeight());
24	}
25
26	if (DEBUG)
27	{
28	Debug->Output();
29	}
30
31	glMatrixMode(GL_PROJECTION);
32	glPopMatrix();
33	glMatrixMode(GL_MODELVIEW);
34	}

1	void objDraw::Sprite(GLuint sprite, GLuint mask, int x1, int y1, int x2, int y2)
2	{
3	glEnable(GL_TEXTURE_2D);
4	glEnable(GL_BLEND);
5	glBlendFunc(GL_DST_COLOR, GL_ZERO);
6
7	glBindTexture(GL_TEXTURE_2D, mask);
8
9	glBegin(GL_QUADS);
10	glTexCoord3f(0, 0, 0); glVertex3f(x1, y2, 0);
11	glTexCoord3f(1, 0, 0); glVertex3f(x2, y2, 0);
12	glTexCoord3f(1, 1, 0); glVertex3f(x2, y1, 0);
13	glTexCoord3f(0, 1, 0); glVertex3f(x1, y1, 0);
14	glEnd();
15
16	glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
17
18	glBindTexture(GL_TEXTURE_2D, sprite);
19	glBlendFunc(GL_ONE, GL_ONE);
20
21	glBegin(GL_QUADS);
22	glTexCoord3f(0, 0, 0); glVertex3f(x1, y2, 0);
23	glTexCoord3f(1, 0, 0); glVertex3f(x2, y2, 0);
24	glTexCoord3f(1, 1, 0); glVertex3f(x2, y1, 0);
25	glTexCoord3f(0, 1, 0); glVertex3f(x1, y1, 0);
26	glEnd();
27	}

1	#include <allegro.h>
2	#include <alleggl.h>
3
4	#include "mouse.h"
5
6	#include "defines.h"
7	#include "globals.h"
8
9	objMouse::objMouse()
10	{
11	visible = false;
12	}
13
14	objMouse::~objMouse()
15	{
16	destroy_bitmap(m_sprite);
17	destroy_bitmap(m_mask);
18	}
19
20	int objMouse::X()
21	{
22	return mouse_x;
23	}
24
25	int objMouse::Y()
26	{
27	return mouse_y;
28	}
29
30	int objMouse::Z()
31	{
32	return mouse_z;
33	}
34
35	int objMouse::LeftButton()
36	{
37	if (mouse_b & 1)
38	{
39	return true;
40	}
41	else
42	{
43	return false;
44	}
45	}
46
47	int objMouse::RightButton()
48	{
49	if (mouse_b & 2)
50	{
51	return true;
52	}
53	else
54	{
55	return false;
56	}
57	}
58
59	int objMouse::MiddleButton()
60	{
61	if (mouse_b & 4)
62	{
63	return true;
64	}
65	else
66	{
67	return false;
68	}
69	}
70
71	BITMAP* objMouse::CursorSprite()
72	{
73	return m_sprite;
74	}
75
76	BITMAP* objMouse::CursorMask()
77	{
78	return m_mask;
79	}
80
81	bool objMouse::Visible()
82	{
83	return visible;
84	}
85
86	int objMouse::CursorWidth()
87	{
88	return m_sprite->w;
89	}
90
91	int objMouse::CursorHeight()
92	{
93	return m_sprite->h;
94	}
95
96	GLuint objMouse::TextureSprite()
97	{
98	return texSprite;
99	}
100
101	GLuint objMouse::TextureMask()
102	{
103	return texMask;
104	}
105
106	void objMouse::SetCursorSprite(const char* filename)
107	{
108	m_sprite = load_bitmap(filename, NULL);
109	texSprite = allegro_gl_make_texture(m_sprite);
110	}
111
112	void objMouse::SetCursorMask(const char* filename)
113	{
114	m_mask = load_bitmap(filename, NULL);
115	texMask = allegro_gl_make_texture(m_mask);
116	}
117
118	void objMouse::Show()
119	{
120	visible = true;
121	}
122
123	void objMouse::Scare()
124	{
125	visible = false;
126	}
127
128	void objMouse::Draw()
129	{
130	allegro_gl_set_allegro_mode();
131
132	draw_sprite(screen, m_sprite, mouse_x, mouse_y);
133
134	allegro_gl_unset_allegro_mode();
135	}