Скачать или смотреть Understanding glDrawElements: How to Use Vertex Color in OpenGL

This guide explores how to leverage vertex color with OpenGL in your graphics applications, detailing the solutions to a common issue faced by beginners: not receiving output when using `glDrawElements`.
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This video is based on the question https://stackoverflow.com/q/64712281/ asked by the user 'Mandar Sadye' ( https://stackoverflow.com/u/6321700/ ) and on the answer https://stackoverflow.com/a/64712469/ provided by the user 'Rabbid76' ( https://stackoverflow.com/u/5577765/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding glDrawElements: How to Use Vertex Color in OpenGL

When diving into the world of OpenGL, you might encounter challenges as you upgrade your graphics application. One such issue is getting no output from the glDrawElements function when attempting to take color data from a Vertex Buffer Object (VBO). Let's break down this problem and provide a clear solution.

The Problem

As a newcomer to OpenGL, you may have started with a basic example that successfully draws shapes using hardcoded color values via uniform variables. However, transitioning to dynamic colors from a VBO can lead to unexpected results. In your case, despite properly binding the color attributes, the expected display on the screen fails when using the color data from the VBO.

The Current Code Explanation

In your code, you are attempting to:

Set vertex positions and colors in a single array.

Use glDrawElements to draw the shape based on this data.

Retrieve and utilize color data through a shader.

Given the setup in the fragment shader, it becomes clear that the input variable in_color is not set correctly for use in your drawing operation. Here's how to adjust your implementation to resolve this issue.

Solution Overview

To effectively use the color data from your VBO, you need to ensure that your vertex shader correctly passes the color information to the fragment shader. Follow these steps to achieve that.

Step 1: Update the Vertex Shader

We will modify the vertex shader to pass the color from the VBO to the fragment shader.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Update the Fragment Shader

Next, ensure that your fragment shader receives the color data from the vertex shader.

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Verify glVertexAttribPointer Calls

Verify the attribute pointer calls in your main OpenGL code base to make sure they correspond to your shader inputs.

Ensure the offset is correct.

Confirm the attribute locations are matching those specified in the shaders.

Your configuration looks correct, so ensure no changes affect this.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By ensuring that the color is properly passed from the vertex shader to the fragment shader, you should see the colors displayed correctly when using glDrawElements. The inclusion of inColor for color attribute handling reinforces understanding how input and output variables can be effectively managed in OpenGL.

As you continue to develop your OpenGL skills, remember that debugging easily becomes easier with state checks and validating shader expectations. Happy coding!