OpenGL doesn't render behind blended texture tris

OpenGL OpenGL: Basic Coding
1

Hello everybody, new member here!
After a few years developing games using engines, I’m super happy to dive into lower level programming!

I came across an unexpected behavior and would appreciate if anyone could help me out:
I’m rendering an image and a rectangle behind it:
[ATTACH=CONFIG]1557[/ATTACH]

Here’s the code (so far, so good):


            glClearColor(1.f, 0.f, 1.f, 0.f);
            glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
          
            
            glBindTexture(GL_TEXTURE_2D, texture_handle);
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, bitmap);
            
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
            glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
            glEnable(GL_TEXTURE_2D);
            
            glBegin(GL_TRIANGLES);
            glColor3d(1.f, 1.f, 1.f);
            
            glTexCoord2f(0.f, 0.f);
            glVertex3f(-0.4f, -0.4f, -0.5f);
            glTexCoord2f(1.f, 0.f);
            glVertex3f(0.2f, -0.4f, -0.5f);
            glTexCoord2f(1.f, 1.f);
            glVertex3f(0.2f, 0.2f, -0.5f);
            
            glTexCoord2f(0.f, 0.f);
            glVertex3f(-0.4f, -0.4f, -0.5f);
            glTexCoord2f(0.f, 1.f);
            glVertex3f(-0.4f, 0.2f, -0.5f);
            glTexCoord2f(1.f, 1.f);
            glVertex3f(0.2f, 0.2f, -0.5f);
            
            glEnd();
            
            
            glBegin(GL_TRIANGLES);
            glColor3d(1.f, 1.f, 0.f);
            
            glVertex3f(-0.3f, -0.3f, 0.5f);
            glVertex3f(0.3f, -0.3f, 0.5f);
            glVertex3f(0.3f, 0.3f, 0.5f);
            
            glVertex3f(-0.3f, -0.3f, 0.5f);
            glVertex3f(-0.3f, 0.3f, 0.5f);
            glVertex3f(0.3f, 0.3f, 0.5f);
            
            glEnd();

However, when I enable blending, the image renders correctly but the rectangle disappears completely!
[ATTACH=CONFIG]1558[/ATTACH]

Code:


            glClearColor(1.f, 0.f, 1.f, 0.f);
            glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
            
            
            
            glBindTexture(GL_TEXTURE_2D, texture_handle);
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, bitmap);
            
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
            glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
            glEnable(GL_TEXTURE_2D);
            
            glEnable (GL_BLEND);
            glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
            
            
            glBegin(GL_TRIANGLES);
            glColor3d(1.f, 1.f, 1.f);
            
            glTexCoord2f(0.f, 0.f);
            glVertex3f(-0.4f, -0.4f, -0.5f);
            glTexCoord2f(1.f, 0.f);
            glVertex3f(0.2f, -0.4f, -0.5f);
            glTexCoord2f(1.f, 1.f);
            glVertex3f(0.2f, 0.2f, -0.5f);
            
            glTexCoord2f(0.f, 0.f);
            glVertex3f(-0.4f, -0.4f, -0.5f);
            glTexCoord2f(0.f, 1.f);
            glVertex3f(-0.4f, 0.2f, -0.5f);
            glTexCoord2f(1.f, 1.f);
            glVertex3f(0.2f, 0.2f, -0.5f);
            
            glEnd();
            
            
            glBegin(GL_TRIANGLES);
            glColor3d(1.f, 1.f, 0.f);
            
            glVertex3f(-0.3f, -0.3f, 0.5f);
            glVertex3f(0.3f, -0.3f, 0.5f);
            glVertex3f(0.3f, 0.3f, 0.5f);
            
            glVertex3f(-0.3f, -0.3f, 0.5f);
            glVertex3f(-0.3f, 0.3f, 0.5f);
            glVertex3f(0.3f, 0.3f, 0.5f);
            
            glEnd();

What am I missing? :confused:

Thanks so much! :slight_smile:
Dan Zaidan

2

Tried calling glDisable(GL_BLEND); before the non-textured triangles.
Now it displays it where the other texture doesn’t render… :confused:

[ATTACH=CONFIG]1559[/ATTACH]


            glClearColor(1.f, 0.f, 1.f, 0.f);
            glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
            
            
            
            glBindTexture(GL_TEXTURE_2D, texture_handle);
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, bitmap);
            
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
            glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
            glEnable(GL_TEXTURE_2D);
            
            glEnable (GL_BLEND);
            glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
            
            
            glBegin(GL_TRIANGLES);
            glColor3d(1.f, 1.f, 1.f);
            
            glTexCoord2f(0.f, 0.f);
            glVertex3f(-0.4f, -0.4f, -0.5f);
            glTexCoord2f(1.f, 0.f);
            glVertex3f(0.2f, -0.4f, -0.5f);
            glTexCoord2f(1.f, 1.f);
            glVertex3f(0.2f, 0.2f, -0.5f);
            
            glTexCoord2f(0.f, 0.f);
            glVertex3f(-0.4f, -0.4f, -0.5f);
            glTexCoord2f(0.f, 1.f);
            glVertex3f(-0.4f, 0.2f, -0.5f);
            glTexCoord2f(1.f, 1.f);
            glVertex3f(0.2f, 0.2f, -0.5f);
            
            glEnd();
            
            glDisable(GL_BLEND);
            
            glBegin(GL_TRIANGLES);
            glColor3d(1.f, 1.f, 0.f);
            
            glVertex3f(-0.3f, -0.3f, 0.5f);
            glVertex3f(0.3f, -0.3f, 0.5f);
            glVertex3f(0.3f, 0.3f, 0.5f);
            
            glVertex3f(-0.3f, -0.3f, 0.5f);
            glVertex3f(-0.3f, 0.3f, 0.5f);
            glVertex3f(0.3f, 0.3f, 0.5f);
            
            glEnd();