iOS OpenGL ES 2.0 Draw 3D Line and Set Color

Question

I can successfully draw lines in OpenGL ES 2.0 on the iPhone with the following code. I am disabling textures and blending but my GLKBaseEffects useConstantColor does not seem to color the line - it is always black! I cannot set the color! How can I do that?

// Turn off texturing
self.effect.texture2d0.enabled = NO;
self.effect.texture2d1.enabled = NO;

// Turn off blending
glDisable(GL_BLEND);
glDisable(GL_TEXTURE_2D);

// Draw a line
self.effect.useConstantColor = GL_TRUE;

// Make the line a red color
self.effect.constantColor = GLKVector4Make(
                                           1.0f, // Red
                                           0.0f, // Green
                                           0.0f, // Blue
                                           1.0f);// Alpha

// Prepare the effect for rendering
[self.effect prepareToDraw];

GLfloat line[] = { -1.0, -1.0, -6.0, 1.0, 1.0, 5.0, 1.0, -1.0, 2.0 };

// Create an handle for a buffer object array
GLuint bufferObjectNameArray;

// Have OpenGL generate a buffer name and store it in the buffer object array
glGenBuffers(1, &bufferObjectNameArray);

// Bind the buffer object array to the GL_ARRAY_BUFFER target buffer
glBindBuffer(GL_ARRAY_BUFFER, bufferObjectNameArray);

// Send the line data over to the target buffer in GPU RAM
glBufferData(
             GL_ARRAY_BUFFER,   // the target buffer
             sizeof(line),      // the number of bytes to put into the buffer
             line,              // a pointer to the data being copied
             GL_STATIC_DRAW);   // the usage pattern of the data

// Enable vertex data to be fed down the graphics pipeline to be drawn
glEnableVertexAttribArray(GLKVertexAttribPosition);

// Specify how the GPU looks up the data
glVertexAttribPointer(
                      GLKVertexAttribPosition, // the currently bound buffer holds the data
                      3,                       // number of coordinates per vertex
                      GL_FLOAT,                // the data type of each component
                      GL_FALSE,                // can the data be scaled
// * INCORRECT *      3,                       // how many bytes per vertex (3 floats per vertex)
                      0,                       // stride (0 bytes between coordinates.) ~Olie
// * INCORRECT *      NULL);                   // offset to the first coordinate, in this case 0 
                      line);                   // pointer to the buffer to draw. ~Olie

// Set the line width
glLineWidth(5.0);

// Render the line
glDrawArrays(GL_LINE_LOOP, 0, 3);

// Turn on blending
glDisable(GL_BLEND);

// Turn on texturing
self.effect.texture2d0.enabled = YES;
self.effect.texture2d1.enabled = YES;

In researching answers for my own (different) problem, I came across this post. One correction: in your sample, above, the 2nd-last parameter in glVertexAttribPointer is stride, and should be 0, not 3. I've edited-in a comment, but not changed the actual code, in case you want to comment, edit or whatever, yourself. Same thing with the last parameter, which is a pointer to the array of coordinates. (One reason I'm slightly hesitant is because I don't know if things work differently when you use bound buffers.) — Olie

junkimu junkimu · Accepted Answer · 2013-05-10T01:53:23

1

votes

Try adding this:

// Turn off lighting
self.effect.light0.enabled = GL_FALSE;

iOS OpenGL ES 2.0 Draw 3D Line and Set Color

1 Answers