alpha blending problem
Author
Hi ppl i have problem with alpha blending.. i succesfully blend bitmap.bmp
and bitmapalpha.bmp for the first time when it is drawed... but every other
time i call my list Tree or any other it doesn''t blend correctly..Plz if
anyone can help here is the code i use...
GLvoid BuildLists()
{
Tree=glGenLists(2);
glNewList(Tree, GL_COMPILE);
glBindTexture(GL_TEXTURE_2D, texture[3]);
glBegin(GL_QUADS); // Start Drawing A Textured Quad
glTexCoord2f(0.0f, 0.0f); glVertex3f(-0.2f, -0.2f, 0.0f); // Bottom
Left
glTexCoord2f(1.0f, 0.0f); glVertex3f( 0.2f, -0.2f, 0.0f); // Bottom
Right
glTexCoord2f(1.0f, 1.0f); glVertex3f( 0.2f, 0.2f, 0.0f); // Top Right
glTexCoord2f(0.0f, 1.0f); glVertex3f(-0.2f, 0.2f, 0.0f); // Top Left
glEnd();
glBlendFunc(GL_ONE, GL_ONE);
glBindTexture(GL_TEXTURE_2D, texture[4]);
glBegin(GL_QUADS); // Start Drawing A Textured Quad
glTexCoord2f(0.0f, 0.0f); glVertex3f(-0.2f, -0.2f, 0.0f); // Bottom
Left
glTexCoord2f(1.0f, 0.0f); glVertex3f( 0.2f, -0.2f, 0.0f); // Bottom
Right
glTexCoord2f(1.0f, 1.0f); glVertex3f( 0.2f, 0.2f, 0.0f); // Top Right
glTexCoord2f(0.0f, 1.0f); glVertex3f(-0.2f, 0.2f, 0.0f); // Top Left
glEnd();
glEndList();
}
int DrawGLScene(GLvoid) // Here''s Where We Do All The Drawing
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glBlendFunc(GL_DST_COLOR,GL_ZERO); // Blend Screen Color With Zero
(Black)
glEnable(GL_BLEND); // Enable Blending
glDisable(GL_DEPTH_TEST); // Disable Depth Testing
glLoadIdentity();
glTranslatef(0.5f,0.15f,-2.0f);
glCallList(Tree);
glLoadIdentity();
glTranslatef(-0.5f,0.7f,-2.0f);
glCallList(Tree);
glEnable(GL_DEPTH_TEST); // Enable Depth Testing
glDisable(GL_BLEND);
}
GLvoid BuildLists(){Tree=glGenLists(2);glNewList(Tree, GL_COMPILE); Why are you generating two lists while you call glNewList()/glEndList() only once???? Try changing to glGenLists(1)
Sander Maréchal
[Lone Wolves Game Development][RoboBlast][Articles][GD Emporium][Webdesign][E-mail]
I got it. It''s pretty simple.
1) you set the blendfunc to GL_DST_COLOR,GL_ZERO
2) you call the list for the first time.
2.1) the first part of the list is rendered with GL_DST_COLOR,GL_ZERO
2.2) in the list you change to GL_ONE, GL_ONE
2.3) you draw the second part with GL_ONE, GL_ONE
3) you translate/rotate some
4) you call the list for the second time
4.1) the first part is drawn with GL_ONE, GL_ONE (it was set above in (2.2) and you didn''t change it back to GL_DST_COLOR,GL_ZERO)
4.2) You change to GL_ONE, GL_ONE. This doesn''t do anything since it is already GL_ONE, GL_ONE.
4.3) you draw the second part of the list
The solution: At the beginning of the list, set the belndmode to GL_DST_COLOR,GL_ZERO
Sander Maréchal
[Lone Wolves Game Development][RoboBlast][Articles][GD Emporium][Webdesign][E-mail]
1) you set the blendfunc to GL_DST_COLOR,GL_ZERO
2) you call the list for the first time.
2.1) the first part of the list is rendered with GL_DST_COLOR,GL_ZERO
2.2) in the list you change to GL_ONE, GL_ONE
2.3) you draw the second part with GL_ONE, GL_ONE
3) you translate/rotate some
4) you call the list for the second time
4.1) the first part is drawn with GL_ONE, GL_ONE (it was set above in (2.2) and you didn''t change it back to GL_DST_COLOR,GL_ZERO)
4.2) You change to GL_ONE, GL_ONE. This doesn''t do anything since it is already GL_ONE, GL_ONE.
4.3) you draw the second part of the list
The solution: At the beginning of the list, set the belndmode to GL_DST_COLOR,GL_ZERO
Sander Maréchal
[Lone Wolves Game Development][RoboBlast][Articles][GD Emporium][Webdesign][E-mail]
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