GLKit Transparent Texture

Question

I am using the following link for source code for drawing a 3D cube in iOS.

http://www.raywenderlich.com/5235/beginning-opengl-es-2-0-with-glkit-part-2

Here is a code snippet of my update routine:

- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect {
glClearColor(30/255.0, 30/255.0, 30/255.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT);

// Enable transparency
//glEnable(GL_BLEND);
//glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

[[self effect] prepareToDraw];

glBindVertexArrayOES(_vertexArray);
glDrawElements(GL_TRIANGLES, sizeof(Indices)/sizeof(Indices[0]), GL_UNSIGNED_BYTE, 0);

// Cleanup: Done with the current blend function
//glDisable(GL_BLEND);

}

I am trying to create a cube with a texture that has transparency, and ultimately draw the underlying faces. I've attached my actual texture. What it looks like right now is a cube showing all faces with no transparency showing the underlying faces. If I uncomment the blend routines, it draws a transparent cube that blends on the background, but the other faces.

Here's part of how I load my texture:

_effect = [[GLKBaseEffect alloc] init];

NSDictionary * options = @{ GLKTextureLoaderOriginBottomLeft: @YES };
NSError *error;
NSString *path = [[NSBundle mainBundle] pathForResource:@"Texture200x200" ofType:@"png"];
GLKTextureInfo *info = [GLKTextureLoader textureWithContentsOfFile:path options:options error:&error];
if (info == nil) {
    NSLog(@"Error loading file: %@", error.localizedDescription);
}
[[[self effect] texture2d0] setName:info.name];
[[[self effect] texture2d0] setEnabled:YES];
[[[self effect] texture2d0] setEnvMode:GLKTextureEnvModeDecal];

The texture is just a poka-dot texture with solid dots and the negative space being completely transparent. I am very new to openGL. Thank you for the help!

I am including a link of what I am trying to accomplish. Just to close to the end, and you'll see how the textures are blending together.

http://www.youtube.com/watch?v=TtK_8sddGaQ

Paul Mikesell Paul Mikesell · Accepted Answer · 2013-07-22T20:21:06

Two things - first, you do in fact need to enable blending. You have this in your code but it's commented out:

glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

Second, I see you're using the GLKit GLKBaseEffect. I've found through trial and error that you have to set the texture env mode to replace, NOT decal in order for transparency to work:

self.effect.texture2d0.envMode = GLKTextureEnvModeReplace;

GLKit Transparent Texture

1 Answers