FontRenderer and basic GL calls

EG1

Draw a text/string

This is under Minecraft context. Don't forget to register event listeners.

RenderGameOverlayEvent is generally considered as a good entry point for screen space HUD rendering.

@SubscribeEvent
public static void onRenderGameOverlay(RenderGameOverlayEvent event)
{
    Minecraft.getMinecraft().fontRenderer.drawString("test", 0, 0, Color.RED.getRGB());
}

• The default rendering pivot is the top-left corner
• GL is a state machine so the color change affects the crosshair

Notice:
Another major reason why GL state leaks here is that Minecraft's FontRenderer is based on the fixed-func pipeline that heavily relies on GL states.
If you implemented a font renderer via shaders (i.e. programmable pipeline), it'll be much safer "states" wise, but the current bounded shader program is also a state, so...

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EG2

Draw a string with state leakage handled

FloatBuffer floatBuffer = ByteBuffer.allocateDirect(16 << 2).order(ByteOrder.nativeOrder()).asFloatBuffer();

GL11.glGetFloat(GL11.GL_CURRENT_COLOR, floatBuffer);
float r = floatBuffer.get(0);
float g = floatBuffer.get(1);
float b = floatBuffer.get(2);
float a = floatBuffer.get(3);
        
Minecraft.getMinecraft().fontRenderer.drawString("test", 0, 0, Color.RED.getRGB());

GlStateManager.color(r, g, b, a);

• Avoid the state leakage by recording the value and restoring it

Notice:

• LWJGL3 provides MemoryStack to get temporary byte buffers so you don't have to allocate and maintain one by yourself
• LWJGL3 provides GL11C to allow easier state queries: you can pass a int[] instead
• Never allocate byte buffers in hotpaths (slow!)
• Don't forget to set order to nativeOrder (aka CPU endianness)
• ByteBuffer.asFloatBuffer() points to the same slice of memory

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EG3

Changing x

Minecraft.getMinecraft().fontRenderer.drawString("test", 10, 0, Color.RED.getRGB());

• X-axis is like our normal x-axis

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EG4

Changing y

Minecraft.getMinecraft().fontRenderer.drawString("test", 0, 10, Color.RED.getRGB());

• Y-axis is upside down

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EG5

Transformation

// push the transformation matrix
GlStateManager.pushMatrix();
GlStateManager.translate(20, 20, 0);
GlStateManager.scale(2, 2, 0);
Minecraft.getMinecraft().fontRenderer.drawString("test", 0, 0, Color.RED.getRGB());
// pop the transformation matrix
GlStateManager.popMatrix();

• We want to use pushMatrix & popMatrix to define the scope of transformation first
• And this is how scale & translate work

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EG6

Transformation order

GlStateManager.pushMatrix();
// notice the order of `scale` and `translate`
GlStateManager.scale(2, 2, 0);
GlStateManager.translate(20, 20, 0);
Minecraft.getMinecraft().fontRenderer.drawString("test", 0, 0, Color.RED.getRGB());
GlStateManager.popMatrix();

• The test moves further because we apply the x2 scale first
• Be careful with the order of scale calls

Contributors

Nullpinter

Last edited about 1 hour ago

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16cf2d7-docs(en, wiki): add renderbook metadata

7ba1bad-docs(en, wiki): add renderbook from https://github.com/tttsaurus/Mc122RenderBook